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【单选题】
有一个静止在磁场中的中性粒子,放出一个电子后使两者在垂直于磁场的平面内运动,则A.
两粒子所受洛仑兹力相同
B.
两粒子的运动速率相同
C.
两粒子作圆周运动的周期相同
D.
两粒子作圆周运动的半径相同
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【简答题】It
costs four times as much to gain a new as it costs to keep an old one.
【单选题】I like this 3G cellphone very much, but it costs almost _______that one.
A.
four times as many as
B.
as four times many as
C.
four times as much as
D.
as four times much as
【单选题】A commonly used rule of thumb is that it costs approximately ____ times as much to get a new customer as it does to keep an existing customer.
A.
three
B.
four
C.
five
D.
six
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