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举一反三
【单选题】在质谱仪中当收集正离子的狭缝位置和加速电压固定时，若逐渐增加磁场强度H，对具有不同质荷比的正离子，其通过狭缝的顺序如何变化？（）
A.
从大到小
B.
从小到大
C.
无规律
D.
不变
【单选题】In July 1994 Jupiter, the largest planet in our solar system, was struck by 21 pieces of a comet (彗星). When the fragments (碎片) landed in the southern part of the giant planet, the explosions were watc...
A.
give an accurate description of the possible disaster in the future
B.
prove that humans will sooner or later be destroyed
C.
tell the historical development of the Earth
D.
warn of a possible disaster in the future