COULD - A physical possibility.

Example: If I were taller, I COULD see over the fence.
(but I wouldn't neccesarily do it!)

MIGHT - A question of chance, but not in your control.

Example: You MIGHT see a tiger, if you went into the forest.
(There is a tiger, there but not everyone sees it.)

WOULD - A sure consequence.

Example: If you jumped in the water, you WOULD get wet.
(At least the person speaking thinks so.)

Note: There are, of course, many sentences where two or
all three answers would fit:

(If I were rich I COULD, WOULD or MIGHT buy a Rolls Royce.)

So a wrong answer is not neccessarily grammatically incorrect,
only illogical.