Both the complexity of the phenomenon known as extinction and the vastness of the biosphere, having prompted many scientists to call for a large increase in the number of biologists working both in the field and in laboratories to clarify the relationships among the planet's many endangered life-forms.

(A) and the vastness of the biosphere, having prompted many scientists to call for a large increase in the number of biologists working both
(B) and the vastness of the biosphere has prompted many scientists calling for a large increase in the number of biologists both working
(C) and the vastness of the biosphere have prompted many scientists to call for a large increase in the number of biologists working both
(D) as well as the vastness of the biosphere have prompted many scientists to call for a large increase in the number of biologists who both work
(E) as well as the vastness of the biosphere has prompted many scientists to call for a large increase in the number of biologists who work both

[spoiler]OA: C[/spoiler]

Is "Both X as well as Y" always wrong?

Please clarify.

Thanks.