I haven't done such a topic for a long time. It's actually very simple to think about it carefully. Just break down the parts, don't think too complicated.

You see, there are three students and four courses, one for each, that is, each person has four choices.

Then a * * * has 4*4*4=64 choices.

① A has four choices, B has three choices and C has two choices, so it is 4*3*2=24 choices.

The probability is 24/64.

(2) I just didn't choose two courses, that is, I only chose two courses. I forgot the formula. Just give me an idea: 1. Choose two elective courses first. 2) Assign these two elective courses to three students.

(3) I forgot what the mathematical expectation of distribution table is. I'm sorry

To sum up: don't be blind when doing mathematical probability problems. It is most important to clear your mind, of course, to see the requirements clearly.