Probably in that case the best answer is B, although other options are also grammatically correct. "Get ready for" and "prepare for" are interchangeable, although "prepare for" is a bit more formal. "Get ready for" and "prepare for" are talking about the future - the person/people are not currently ready - there are still things to do before they are ready. If they "are ready" that is the present, they do not need to do anything further.

All of them are strictly grammatically correct, I think. BUT - It is not natural to use simple present tense for expressions like this. So the only options are B or D. Which of those is correct depends on prior knowledge, and social expectations. I guess, since you are from China, that the students are expected to study so D is the most likely answer. But - I also don't believe that a student asked this question. And if it's a question that you are asking your students, I think you should think of a better question.

Yes. I am an English teacher in China. That is a question from my student.

Is this a class question? If it is, it's a pretty stupid one... All are strictly correct, but only two are natural, and which of those is correct depends on prior knowledge, or guesswork.