Inreview of 44 studies, American researchers found that men and womenwho ate six key food

In review of 44 studies, American researchers found that men and women who ate six key foods daily cut the risk of heart disease by 76%.
A. a; the
B. the; a
C. a; 不填
D. 不填； a

A. a; theB. the; a(答案→)C. a; 不填D. 不填； a解析： 一份44个研究课题组成的调查显示，故第一空选冠词a;第二空 heart disease（心脏病）习惯上不用惯词。

就是这个解释