I think _________ necessary for students to take an interest in all subjects.

Lily,______ do you study for a math best? —By asking my teacher for help.

Sally, can you ______ the notebook here? — Yes, I can．

He ran the 100 meters in 9.91 seconds, and I have not seen _________ this year.

Is that Lucy’s sister, Lily?—No, it _______ be her. She has gone to English.