This is really not a simple topic. The first question of the (1) subproblem is relatively simple. After analysis, there is an answer AC, just fill in the blanks; The second question is not difficult, just set the coordinates of d and list a very simple inequality to solve according to the meaning of the question.

The second question is really enough to drink a pot, so we must follow a famous saying: there is a picture with the truth. Only by analyzing the images can we get the answer.