What is the weak dimension of a nonzero right module M over a ring R?

A. The number of relations between the generators of the module M
B. The smallest number n such that the Tor group Tor_n^R(M,N) is nonzero for some left R-module N
C. The number of generators of the module M
D. The largest number n such that the Tor group Tor_n^R(M,N) is nonzero for some left R-module N
Answer: 