______________ is the center of our planetary system was a difficult concept to grasp in the Middle Ages.
A. It is the sun and not the earth B. Being the sun and not the earth
C. The sun and not the earth D. That the sun and not the earth
I was so angry at all _____ he was doing _____ I slapped (抽) his face.
A. what; that B. which; that C. that; that D. that; so
That is the reason _____I refused it.
A. why B. for that C. because D. which
The tables and pictures help make ________ clear ________I wasn't sure of before.
A. it; for me to understand what B. it; everything
C. everything; to understand what D. /; what
really matters is not whether you succeed or not，but rather whether you’11 try or not.
A. What B. Whether C. If D. Which
—The experiment is of particular importance.
—I see. We will carry on with it ________ we can get enough money.
A. unless B. though C. whether D. until
