If we add the prefix '-UN’ to some words in English, we can...

If we add the prefix '-UN’ to some words in English, we can get the opposite of that word, like in ‘unwanted’ (l. 29). In this sense, consider the following words and analyze them:

I. able.

II. happy.

III. fair.

IV. acceptable.

Which of them can be an opposite just by adding the prefix ‘-UN’?