下列物质中属于纯净物的是（　　）

A．二氧化碳

B．新鲜的空气

C．矿泉水

D．石灰石

（2）语法填空

I was being tested for a driving license ___1___ the third time. I had been asked to drive in heavy traffic and had done so ___2___(succeed). After ___3___ (instruct) to drive out of town, I began to acquire confidence. Sure that I had passed, I was almost beginning to enjoy ___4___ test. The examiner must have been pleased with my ___5___(perform), for he smiled and said. “Just one more thing, Mr. Eames. Let us suppose that a child suddenly crosses the road in front of you. As soon as I tap on the window, you must stop ___6___ five feet.” I continued driving and after some time, the examiner tapped loudly, ___7___ the sound could ___8___ (hear) clearly, ___9___ took me a long time to react. I suddenly pressed the brake pedal(刹车踏板)and both of us were thrown forward. The examiner looked at me sadly. 'Mr. Eames,' he said, ___10___ a mournful voice, “you have just killed that child!”