OG SC#

[extroversion]

Studies of the human "sleep-wake cycle" have practical relevance for matters ranging from duty assignments in nuclear submarines and air-traffic control towers to the staff of shifts in 24-hour factories.

(A) to the staff of
(B) to those who staff
(C) to the staffing of
(D) and staffing
(E) and the staff of

why the best answer is C ?
I agree that C sounds best. But why is staff in answer choice A also not parallel? Is it because assignments and staffing are action nouns whereas staff is not?

[mrsmarthi]

I think this sentence is testing the idiom - range from X to Y.

X = duty assignments (noun)
Y should also be parallel to the work related nouns. And that is clear in C - The staffing of shifts.

[extroversion]

Thanks a lot =)