1．Carbon dioxide, which makes a ________ between us and the sun, prevents heat from getting out of the atmosphere easily, so the earth is becoming warmer.
A．difference B．comparison
C．connection D．barrier
D 解析：句意：二氧化碳是我们和太阳之间的一道屏障，它使地球上的热量不容易释放出大气层，于是地球就变得越来越暖和。 difference“分歧，区别”； comparison“比较”； connection“联系”； barrier“障碍，屏障”。语境说地球的热量因二氧化碳而不容易释放出大气层，因此这里选D, 表示“障碍，屏障”。
2．—I’ m surprised to hear that Sue and Paul have ________．
—So am I. They seemed very happy together when I last saw them.
A．broken up B．finished up
C．divided up D．closed up
A 解析：句意：——听到Sue和Paul分手的消息我很吃惊。——我也是。我上次看到他们的时候，他们在一起似乎很幸福。 break up“破裂；分手”。
3．It is not ________ to discuss the question again and again.
A．worth B．worthy
C．worthwhile D．while
C 解析：It is worthwhile to do sth. 为固定句型，意为“做某事是值得的”。
