----Can he work out the maths problem?----I think _____ hard for him to work it out.
Look! They ________ in the hallway.
Can you help me ________ my homework?
The teachers ________ on the blackboard with chalk in the future.
- ________ book is this? -- It's Mary's.
There ________ some tomatoes and milk in the box, but now there aren't any.