Only when _____ possible to settle the problem how to get the machine repaired.

Bob， __________ my teacher, Miss Hu. Miss Hu, ___________ my brother.

The pet dog in your hand is very nice. Is it ?–Yes, but I’ll give it to my friend, Lucy, as birthday present.

I feel tired and sleepy. —Why not stop ______?

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