34. Beyond the immediate cash flow crisis that the
museum faces, its survival depends on if it can
broaden its membership and leave its cramped
quarters for a site where it can store and exhibit its
more than 12,000 artifacts.
(A) if it can broaden its membership and leave
(B) whether it can broaden its membership
and leave
(C) whether or not it has the capability to broaden
its membership and can leave
(D) its ability for broadening its membership
and leaving
(E) the ability for it to broaden its membership
and leave
正确答案B没问题，但是我想请问各位NN，什么时候用if，什么时候用whether，有什么说法吗
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