I don’t know when my son __________back, but when he __________back ,I’ll give you a call

Please sit_____ your chair and listen_____ the teacher. [ ]

Hey, Jack. You ________ on the phone just now. But you weren’t here and the man left a phone number. —Oh? I was in the library.

The young boy found ________ hard to finish the work alone.

This morning our head teacher came to school _________ than ________ student in our class.