No one ___________ for a drive, because the weather is so bad.

Math is too difficult. I want to give it up. —Please don’t. Nothing is _________if you put your heart into it.

I don’t know when my son __________back, but when he __________back ,I’ll give you a call

Many scientists say that it’s important for us to have ______ food in our diet.

It is usually warm in Nanjing in spring. But sometimes it be very cold.