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 |
.
It’s already 10’clock. I wonder how it______that she was two hours late on such a short trip.
| A．came over | B．came out | C．came about | D．came up |
.
Much__________he has a good taste, he can’t avoid being influenced by advertisements.
| A．that he claims | B．does he claim |
| C．as he claims | D．is it that he claims |
.
It is what you do rather than what you say____________really matters.
| A．that | B．what | C．which | D．this |
.
—Must I turn off the gas after cooking?
—Of course! You can never be__________careful with that.
| A．enough | B．too | C．so | D．very |
.
____________apple fell from the tree and hit him on_____________head.
| A．An; his | B．An; the | C．The; his | D．The; the |