—Who______ it be that is knocking at the door? —It ______ be Father, but I’m not sure.
The doctor will not permit mother up __________ her leg is better.
Either his wife or his friends __________ his birthday party.
No one knows __________ it will be fine tomorrow and __________ we can play basketball together.
Loulan is believed __________ over by sandstorms gradually from AD200 to AD400.
They were having an argument about __________ turn it was to do the cooking.