Choose the best topic sentence from the four options below.
Passive smokers may easily catch the diseases active smokers invite.
Passive smoking is becoming widely recognized as a major health hazard.
Researchers find that secondhand smoke increases one’s risk of lung cancer.
Passive smoking refers to the secondhand smoke that nonsmokers breathe in.
A.C.D 过于具体。作为主题句，应该总领整个段落或文章。
