—Why does Mary look so worried today?—I’m not sure, but she _____ a small accident driving here.

 — The socks must be Linda’s.— No, they         be. They’re too small for her.

—Where is Zhang Hua? Is he in the classroom now?—He          be there, for I saw him in the teachers’ office just now.

You _______ see a dentist when you have a toothache. 

In China's countryside, villagers often have the same family name, but ________ not be closely related.