Smoking is one of the causes of cancer,killing millions of people each year.
A. major
B. similar
C. mercial
D. chemical
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(答案→)A. major
B. similar
C. mercial
D. chemical
解析:本题考查形容词辨析。Major主要的;similar相似的; mercial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。