because a. has a compound subject (swimming and golifing)

b. has is a sentence fragment.

c. has a compound predicate (washed and ironed…sandy is the subject)

d. can also be considered the compound predicate

but it doesn’t share the same subject so the answer is C.

this better explains compound predicates for you:

http://www.kwiznet.com/p/takeQuiz.php?ChapterID=486&CurriculumID=15

A and B are obviously wrong because (as pointed out above) they have compound subjects, not compound predicates.

The reason the answer is not D is because the two parts of a compound predicate must share the same subject.