Excerpt from The Care and keeping of Big Cats Part B Kate McConnaughey

(10) One function of zoos being to provide safe places where endangered animals can breed.
Look at the underlined section marked (10).

Choose the answer that best corrects this sentence, if appropriate.

A)
Correct as is
B)
A function of zoos provides safe places where endangered animals can
breed.
C)
One function of zoos to provide safe places where endangered animals can
breed
D)
One function of zoos is to provide safe places where endangered animals
can breed