Discuss whetehr or not:

(a) R2 is a subspace of R3 over R

(b) {(0,0,0)} is a subspace of R3 over Q

(c) Q3 is a subspace of R3 over R

(d) RxQx{0} is a subspace of R3 over Q

I understand the requirements of a subset; however, I do not understand what it means for a set to be over say R. What does this mean and how does it play into deciding if one set is a subspace of another?