题目

In spite of repeated wrongs done to him, he looks _____ to people greeting him.A. friendly              B. lively                 C. worried                D. cold 答案：A设集合A={4，5，7，9}，B={3，4，7，8，9}，全集U=A∪B，则集合∁U（A∩B）中元素个数为    ．