As announced by the course staff, we may get 0/100 for this assignment. I checked my answers, and according to the real-time checking, all answers are correct, but I got 0/100 more 15 times. This is the grader error:
I am sorry. It was my bad. I found the error and fixed. First, since it was mentioned that we may get 0/100, I thought it is the grader problem, Thank you.