新SAT语法练习题及答案(3)

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　　Scientists have been launching cometary missions since 1978. The first one, a joint mission by the European Space Agency and the National Air and Space Administration (NASA) , was a “flyby” in which the spacecraft collected data while passing around Comet Giacobini-Zinner. However, the landing of the Rosetta space probe on comet 67P/ Churyumov-Gerasemenko in 2014 was different: it marked the first time that a probe landed on a comet and giving scientists an unprecedented opportunity to study the surface of a comet. In order to continue this valuable research, additional missions are needed; thus, it is critical that more funding be allocated for this purpose.

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