The word “it” in paragraph 5 refers to __________. A. urban smog B. the ozone hole C. acid rain D. a clean-up agent
The word “it” in paragraph 5 refers to __________.
A. urban smog
B. the ozone hole
C. acid rain
D. a clean-up agent
The word “it” in paragraph 5 refers to __________.
Chọn D