Smoking is one of the causes of cancer killing millions of people each year. A. majorB. si

问题补充：

Smoking is one of the causes of cancer，killing millions of people each year.

A. major

B. similar

C. commercial

D. chemical

答案：

(答案→)A. major

B. similar

C. commercial

D. chemical

解析：本题考查形容词辨析。Major主要的；similar相似的； commercial商业的；chemical化学的。句意：吸烟是引发癌症最主要的原因之一，每年致死数百万的人。故选A。