Answer:
C: are smaller than my wife's.
Explanation:
First, it is necessary to correct the concordance between the subject and the verb. The subject My expenses is plural and requires a plural verb: are. Second, the correct comparative for expenses is smaller than (he expends less than his wife). The comparison is between what he expends and what his wife expends , not comparing his wife. So, it's necessary the apostrophe and s: my wife's
