由于事件A发生的次数至少为0,至多为n,因此事件A的频率范围为______.
由题意可得,事件A为随机事件,故事件A的频率范围为[0,1],
故答案为[0,1].
读一读,选词填空。
1. It's time ____________ (to / for) go to school.
2. It's time ____________ (to / for) go home.
3. What time ____________ (is it / are they)?
4. I can see two ____________ (clock / clocks).
5. School is ____________ (over / ready).
下列信号由180°射频脉冲产生的是
A.自由感应衰减信号B.自旋回波信号C.梯度回波信号D.质子密度信号E.弛豫加权信号