Complete and balance the following half-reactions:

A. Mo3+(aq)→Mo(s) (acidic solution)

B. H2SO3(aq)→SO2−4(aq) (acidic solution)

C. Complete and balance the following half-reaction:
NO−3(aq)→NO(g)(acidic solution)

D. Complete and balance the following half-reaction:
O2(g)→H2O(l)(acidic solution)