第六篇

• 1、

  Paragraph 3 ________

• 2、

  Paragraph 4 ________

• 3、

  Paragraph 6 ________

• 4、

  Paragraph 7 ________

• 5、

  In the twentieth century, soot ________.

• 6、

  Hansen cautioned that greenhouse gases ________.

• 7、

  Black soot covered snow and ice ________.

• 8、

  A soot forcing is unusually effective, which _____