People should __________ from __________ down the trees to protect the earth.

 ---There’s too much salt in the Chinese diet. ---So there is. The WHO says only 1.5 grams of salt __________ for each man every day.

 The girl was often heard ______ happily in her room.

This pair of socks ______ worn out. I'll have to buy a new ______.

They are looking forward to _____________ to the lecture by the famous professor.