---Look at the boy running on the playground. Is it David? ---It ______ be him. I saw him go to the teachers’ office just now.

He _______ have completed his work；otherwise, he wouldn’t be enjoying himself by the seaside.

--Would you like to visit Kun Ming by yourself this summer vocation? --I’m not sure. I _____go there with my parents because of the terrible thing at the railway station.

—Why don’t you wear your jogging shorts, mum?—Well, my legs are too skinny, if you ______ know. 

My neighbor was like a cat on hot bricks before her driving test.