Confusion with plural form

[Mayur Sand]

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

A. in measuring the movements of the Sun and Moon is evidenced not only at

B. in measuring the movements of the Sun and Moon are evidenced not only at

C. in measuring the movements of the Sun and Moon is evidenced at not only

D. to measure the movements of the Sun and Moon is evidenced at not only

E. to measure the movements of the Sun and Moon are evidenced not only at

My pick was (A) but OA is(B) , please explain

[myohmy]

It's pretty simple.

"Evidenced" refers to "the skill" and "the precision."

Since there are two nouns (skill and precision) we have to use "are evidenced" rather than "is evidenced."

Hope that helps!