下列各句中，没有语病的一句是(　　)

Our class ____ more than 50 students. [ ]

Most of us believe that there should be a(n) ______ of mutual(相互的) trust and respect between teachers and students in teaching.

Have you ever been to the Grand Canyon– Yes. I __________ there last summer with my parents.

_____ do you go to the nursing home— Twice a week. We clean their rooms and do some shopping for them.