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参考解析：
刷刷题刷刷变学霸
举一反三
【单选题】Passage Four Initial voyages into space introduced questions scientists had never before considered. Could an astronaut swallow food in zero gravity To keep things simple, astronauts on the Project ...
A.
was an unusual problem among astronauts
B.
was what puzzled the early scientists
C.
caused new problems in space flights
D.
drew the attention of the general public