Smoking is one of the of heart disease and it kills lots of people every year.
A. causes
B. reasons
C. excuses
D. results
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(答案→)A. causes
B. reasons
C. excuses
D. results
解析：词义辨析。A. 引起的原因 B. 理由；理性 C.接口；理由 D. 导致的结果。句意：吸烟是引起心脏病的原因之一，每年致死很多人。结合语境可知选A。