Once a decision has been made, all of us should ________ it.[ ]

______is now no doubt ________ global warming is a security threat to us all

May we leave the classroom now — No; you _____. You ______ to leave until the bell rings.

Shall we go out for a walk—Sorry．I’m too busyto forthe moment．

The last story ________ our teacher told us the other day was ________ of an Italian explorer.