Whenever you are to walk on the ice , that it is solid and safe enough.
It’s no good ________about his grades.
If he ________tomorrow, I could talk to him about it.
Ann is said ________ research in Africa, and she will come back next month.
The old man lived in a house, in front of which _____ with a history of 100 years.
I hope to do now is go home and have a good rest.