You said that you have the answer sheet for these tests. Please tell us what the answer sheet says is the correct answer for each question and give us the explanation which you say is too short. Then tell us why you don't understand the explanation or the correct answer and tell us which answer you would have chosen if you hadn't had the answer sheet. After that, we can try to help you understand them.
See my corrections above, marked in red.
Student or Learner