This machine is very easy （ ）. Anybody can learn to use it in a few minutes.
（A）operating
（B）to be operating
（C）operated
（D）to operate
Birds’ singing is sometimes a warning to other birds （ ） away.
（A）to stay
（B）staying
（C）stayed
（D）stay
The party will be held in the garden, weather （ ）.
（A）permitting
（B）to permit
（C）permitted
（D）permit
