(年北京市西城区高三5月二模试题)31. A person who has never tasted bitter won’t know ______ sweet is.
What ______ heavy snow. Let's go out for a walk in ______ snow, shall we?
It is pleasant to play ______ game of ______ table tennis ______ summer afternoon.
When we saw his face, we knew _____ was bad.
Biology is _____.
____ of them knew about the plan because it was secret.