So far, all of the infected people are thought the flu after direct contact with sick bir

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(答案→)A. to have caught
B. having caught
C. to catch
D. being caught
解析：考查句型：Sb/sth is thought to do/to have done…某人/某物据认为正在做…/已经做…,如果不定式的动作是将要发生，用一般式，如果不定式的动作是先于主句的动作发生，用不定式的完成式，句意：到现在为止，所有的感染的人都被认为是在直接和病禽有过接触。选A。