【正文】
. _____from space , the earth , with water _____seventy percent of its surface , looks like a blue ball. A. Seen 。 covering 3. People always shake hands with each other when _____. A. to introduce B. introduce C. introduced D. introducing 4. _____, tears ran down her pale face. A. No word said B. Say no word C. Not saying a word D. Without saying a word 5. We must take measures to prevent our earth _____. A. to be polluted B. from polluting C. from being polluted D. from polluted 6. As the stone was too heavy to move , I left it _____ on the ground . A. laying B. lay C. lying D. lain. 1—6 CDCAC C