How should the underlined portion of this sentence be changed, if at all?
one hundred bushels of wheat is a good yield.
no change
bushels of wheat are a
bushels of wheat has a
bushels of wheat were a

bushels of wheat are a

Explanation:

the apollo program, also known as project apollo, was the third united states human spaceflight program carried out by the national aeronautics and space administration (nasa), which succeeded in landing the first humans on the moon from 1969 to 1972.