I couldn't have come OR I couldn't come

Hi,

The answer is choice b. Because he was not able to come over due to any reason (- certain action in the past).

Choice a is the structure (could +have pp) that shows the possibility and probability of an action in the past.

Example:

Boy: after picking the cherry, I jumped down the tree.

Father: why did you do that? You could have broken your leg (but you did not) or you could have lost your life for nothing (but you did not).

Hi back,
Modal auxiliary + verb has several usages. One is the real sense of the modals, their dictionary meaning, like (can= be able to), (must=obligatory action)
However, there is another usage for the modal auxiliary when they do not mean the dictionary meaning but they show the inferences you make for an event. There are three tenses in this usage, e.g.,
Simple Present inference:
The man standing there is wearing a jacket and tie. He must be the teacher.
Must here means most probably he’s our teacher.
Or you may say, he can't be the waiter.
Can't here does not mean ability but the least possible probability for being the waiter.
Present continuous inference:
I had a date with John at 9. It is 8:50 now. I called him and he is not at home now.
He must be coming now.
Here must does not mean obligatory action but it shows the strongest possibility and inference that he is coming here now.
Past inference:
The street is wet. It must have rained last night.
Here must shows the strong probability and inference that the wet street is due to the last night raining.
The degree of probability and inference is shown by the use of the modals here. The order is that must is the most probable one and can't is the least probable inference about an action about present (no. 1) and about past (no 3).
For probabilities less than must you can use could, then may, and the less probable than all is might before can't. So you can translate them like this:

زمين خيسه. به احتمال زياد بايد ديشب بارون اومده باشه.

The use of the above modals has nothing to do with their dictionary meanings. But the order from must to can't only decreases the degree of one's certainty on the predicate.
I hope it is clear enough.