Answer: C. Avoid
Step-by-step explanation:
Amiss means, to be out of order or not really right. The miss in amiss, is a clue itself about the word.
Judging from the definition, improper is probably the closest thing to amiss. Improper means not the same as others, which is similar to amiss which is out of place.
The second closest is incorrect (I think you meant incorrect). This basically means the wrong answer, or not what was looked for.
The third closest is unsuitable, which means doesn't match/fit, or not appropriate to the others.
The past 3 have some similarity with amiss but avoid is different.
Avoid means purposefully not involving with something, keeping yourself from doing something. Avoiding something can be a result of finding something amiss, but something out of place doesn't mean that it has to be avoided. Avoiding something is holding back from something which isn't similar to amiss.
Hope that helped a lot.
:)