Either you or I _____going to the teachers‘ office after class.

On her way home, Lucy saw a thief ______ in a shop.She stopped ______ 110 at once.

No one ________ enter this building without the permission of the security guard.[ ]

The first thing _____ I should do is to work out a study plan for the next term.

Tom gave Helen an apple in exchange for a piece of cake.