The North American
(B) moose's long legs enable it to move quickly through the woods, stepping easily over downed trees while predators pursuing them must leap or go around
(C) moose's long legs enable it to move quickly through the woods and to step easily over downed trees, but predators pursuing them must leap over or go around them
(D) moose has long legs, enabling it to move quickly through the woods and to stop easily over downed trees while predators pursuing them must leap or go around

them has no logical antecedent.

The North American
(A) moose's long legs enable it to move quickly through the woods, stepping easily over downed trees, but predators pursuing it must leap or go around them
(E) moose has long legs that enable it to move quickly through the woods, stepping easily over downed trees while predators pursuing it must leap over or go around them

Use appropriate preposition with leap, which is over.

Furthur, subject pronoun (it) referring to moose is better -- though not incorrect-- than subject pronoun referring to moose's( possessive)

In the following OG 16 OA, subject pronoun(she) refers to Elizabeth Barrett browning's-

Although she was considered among her contemporaries to be the better poet than her husband, later Elizabeth Barrett Browning was overshadowed by his success.

A, Although she was considered among her contemporaries to be the better poet than her husband, later Elizabeth Barrett Browning was overshadowed by his success.
B, Although Elizabeth Barrett Browning was considered among her contemporaries as a better poet than her husband, she was later overshadowed by his success.
C, Later overshadowed by the success of her husband, Elizabeth Barrett Browning's poetry had been considered among her contemporaries to be better than that of her husband.
D, Although Elizabeth Barrett browning's success was later overshadowed by that of her husband, among her contemporaries she was considered the better poet.
E, Elizabeth Barrett Browning's poetry was considered among her contemporaries as better than her husband, but her success was later overshadowed by his husband.
OA D

Please note that in OA to this OG 18's SC, comma verbing modifies the last action (to move) and is applied to its subject( moose).
(E) The North American moose has long legs that enable it to move quickly through the woods, stepping easily over downed trees while predators pursuing it must leap over or go around them.
How?
How the moose moves quickly through the woods?
by stepping easily over downed trees.
Who?
Who is stepping over downed trees?
moose (subject of move)

Here is another official SC(from GMAT prep) in which comma verbing modifies the last action and is applied to its subject( subject/ agent performing that action).

Among lower-paid workers, union members are less likely than nonunion members to be enrolled in lower-end insurance plans imposing stricter limits on medical services and requiring doctors to see more patients, and spend less time with each.
(A) imposing stricter limits on medical services and requiring doctors to see more patients, and spend
(B) imposing stricter limits on medical services, requiring doctors to see more patients, and spending
(C) that impose stricter limits on medical services, require doctors to see more patients, and spend
(D) that impose stricter limits on medical services and require doctors to see more patients, spending
(E) that impose stricter limits on medical services, requiring doctors to see more patients and spending
OA D

[spoiler](D) [/spoiler]that impose stricter limits on medical services and require doctors to see more patients, spending less time with each

Other errors-

The North American
(B) moose's long legs enable it to move quickly through the woods, stepping easily over downed trees while predators pursuing them must leap or go around (what?)
(D) moose has long legs, enabling it to move quickly through the woods and to stop easily over downed trees while predators pursuing them must leap or go around( what?)

over what must predators leap?
around what must predators go?
predators must leap over or go around something.
right?
that something you have to mention explicitly.
you cannot omit it!

Here is another official SC with the same type of an error-

In California, a lack of genetic variation in the Argentine ant has allowed the species
to spread widely; due to their being so genetically similar to one another, the ants
consider all their fellows to be a close relative and thus do not engage in the kind of
fierce inter-colony struggles that limits the spread of this species in its native
Argentina.
A. due to their being so genetically similar to one another, the ants consider all their
fellows to be a close relative and thus do not engage in the kind of fierce inter-colony struggles that limits
B. due to its being so genetically similar the ant considers all its fellows to be a close
relative and thus does not engage in the kind of fierce inter-colony struggles that limit
C. because it is so genetically similar, the ant considers all its fellows to be close
relatives and thus does not engage in the kind of fierce inter-colony struggles that limits
D. because they are so genetically similar to one another, the ants consider all their
fellows to be close relatives and thus do not engage in the kind of fierce inter-colony struggles that limit
E. because of being so genetically similar to one another, the ants consider all their
fellows to be a close relative and thus do not engage in the kind of fierce inter-colony struggles that limits
OA D

C. because it is so genetically similar, the ant considers all its fellows to be close relatives and thus does not engage in the kind of fierce inter-colony struggles that limits...
similar to what?
(more discussion here https://www.beatthegmat.com/argentine-ant-t96849.html ).

(C) moose's long legs enable it to move quickly through the woods and to step easily over downed trees, but predators pursuing them must leap over or go around them

Both them are in the same clause and must have the same antecedent--> problematic!

(C) moose's long legs enable it to move quickly through the woods and to step easily over downed trees, but predators pursuing them must leap over or go around them
(D) moose has long legs, enabling it to move quickly through the woods and to step easily over downed trees while predators pursuing them must leap or go around

correct structural parallelism but problematic logical parallelism.

PS:
You made a typo in D-

(D) moose has long legs, enabling it to move quickly through the woods and to stop easily over downed trees while predators pursuing them must leap or go around

not stop but step ; )