Verbal or transitive arguments to 对
b) is not necessarily better than a). They represent different things.


a), 對聼音樂感興趣, means that you have an interest in listening to music.

b), 對音樂感興趣, means that you have an interest in music generally. It could be composing music, playing a musical instrument, or singing. 

In this case, it depends on what you are trying to say. If you like listening to music, a) is correct. If you like music generally, b) is correct. None of them is grammatically better than the other.


Again, g) and h) are both correct, depending on what you say.


g), 對學漢語感興趣, means that you have an interest in learning Chinese.

h), 對漢語感興趣, just means that you have an interest in Chinese generally.


There's a totally different case for your last example involving answers d), e), and f).


d), 對游泳感興趣, is correct. You have an interest in swimming.

e) and f), 對游/泳感興趣, do not make sense at all. 游 and 泳 must be used together to form a term. If you use only one word (in this case), it wouldn't make sense. If you were saying "I threw a snowball", you wouldn't say "I threw a snow" or "I threw a ball".