The cost of organic food is higher than _____ of conventional food because the organic price tag reflects more closely the true cost of growing the food．

When I try to find _______ that prevents so many people from taking part in the program,it seems to me that there are two main causes.

What are you going to give your mother for her birthday—I’m not sure. But I’ll buy her .

I think there will be ______tall buildings and there will be ____pollution in the future.

Are you sure that the news is true-Yes. It be true because the headmaster told me just now.