根据句意，用所给动词的适当形式填空。
We celebrate Christmas by _______ (send) cards to each other.
We should do as much as we can __________ (help) them out of trouble.
The whole class ___________ (divide) into four groups.
How much did you spend _________ (buy) the new bike?
The Green family __________ (have) supper at the table when I came into the house.