---- How often does the train run to Beijing ?----- ________ twenty minutes.
____ you are, _____ mistakes you’ll make.
________all the stars, the sun is __________to the earth.
.I bought _______ exercise books with ________ money.
The harder you study, __________grades you’ll get.
---Do you mind _________your room? ---No, I’ll do that after finishing _________this article.