问题
选择题
Attention, please. All mobile phones must before the meeting starts. [ ]
A. turn
B. be turned off
C. be turning
答案
答案：B
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Attention, please. All mobile phones must before the meeting starts. [ ]
A. turn
B. be turned off
C. be turning
答案：B
（老年抚养比是指人口中非劳动年龄人口数中老年部分对劳动年龄人口数之比）和少儿抚养比
（人口中少年儿童人口数与劳动年龄人口数之比）图。
