Is the OA B?

not only at is parallel with but at

C & D use at not only . Out

The skill and the precision of the Anasazi in measuring the movements of the Sun and Moon is evidenced not only at Chaco Canyon but at a number of other sites.

I removed the phrase in between as its the middleman.

Skill and Precision is compound subject. So use are. A is out

Skill and precision of the anasazi to measure is awkward. E & D are out

B remains

hmm answer is "b" but i am still stuck between B and E...how is "to measure " awkward...isnt it more concised than "in measuring"...m still confused...

Read it like this after removing the "ancient inhabitants of the Southwest"

The skill and the precision of the Anasazi in measuring the movements of the Sun and Moon is evidenced not only at Chaco Canyon but at a number of other sites.

The skill and the precision of the Anasazi to measure the movements of the Sun and Moon are evidenced not only at Chaco Canyon but at a number of other sites.

to measure sounds like (I know we should avoid sounds like ) a future work and has not been done. If it's a work that has not been completed, how can we see it.

B is the choice between B & E because B is using 'measuring' instead of 'to measure'.
'ing' form is preferred because with skills it is always 'ing' form which is right to use.
you will never find "skill to swing" .. it will be "skill in/at swinging"
there r many more similar examples.

So, this usage makes E unidiomatic when B is not.

Example in support of {B} : Brian is more skilled in Programming than in Testing.

So, {E} has an idiom issue

{B} is correct

Ans. B