I need help! SC

[LukeC303]

In Alexandria in 1879, Rodriguez et al is founding a library at which 10,000 books had been stored.
(A) is founding a library at which 10,000 books had been stored
(B) founded a library in which 10,000 books were stored
(C) founded a library that stored 10,000 books
(D) founded a library that had stored 10,000 books
(E) is founding a library by which 10,000 books are stored

Can anybody explain that what's the difference between (B) and (C)? The correct answer is (B).

[RonPurewal]

please read the forum rules before posting!

per those rules, we need a citation of the original source of this problem.

thanks.