【题目】The findings support another study which showed that being happy ______ reduce the risk of heart disease.
A.need
B.shall
C.must
D.can

【答案】D
【解析】考查情态动词。句意：这个发现支持了另一项研究：快乐可以降低心脏病的风险。Need需要;shall将，会;must必须;can可能，可以；根据句意，选D项。