largest and oldest living organism

[msbelasco]

Scientists have recently discovered what could be the largest and oldest living organism on Earth, a giant fungus that is an interwoven filigree of mushrooms and rootlike tentacles spawned by a single fertilized spore some 10,000 years ago and extending for more than 30 acres in the soil of a Michigan forest.

(A) extending
(B) extends
(C) extended
(D) it extended
(E) is extending

Can someone please explain to me how and why you would choose the answer A over all the others. Specifically why can it not be b or e. Thanks.

[Kasia@EconomistGMAT]

The underlined word is a part of a parallel structure "spawned by a single fertilized spore some 10,000 years ago AND extending for more than 30 acres" and, therefore, it should be grammatically and logically parallel with the word "spawned."

"Spawned" acts here as an adjective.
A - correct because "extending" is also used as an adjective and it is logically parallel with "spawned"
B - incorrect, "extends" is a conjugated verb
C- incorrect for the same reason as B
D - "it extended" changes the second part of the parallel structure into a clause, so it is incorrect to compare an adjective with a clause
E - incorrect, 'is extending" is a conjugated verb