Why did _____ take Aunt Alice almost an hour to get home ? —I don’t know . Maybe there was something wrong with her car .

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

Don’t walk _____ the bridge. It’s very dangerous. [ ]

Liu Hua often helps her sister__________lessons.[ ]

I can remember well some pictures and the persons I saw in the room.