_____ it rain tomorrow, we would have to _______ the picnic.
Could people become infected ____ HIV by swimming in a pool or sitting in a bath?
There are too many difficulties for us _______ . We really don’t know _______ to do.
Who do you think is the greatest man _______?
________ is mentioned(提及) above, the number of the students in senior high schools is increasing.
They love their daughter so much that they are always ready to do everything they can ________ her happiness.