RRU电源线屏蔽层接地，若电缆长度超过（）米，需在电缆中间部分加做一处防雷接地。
A.80
B.70
C.60
D.50
参考答案：B
已知f（x）=x2-2x，g（x）=mx+2，对∀x1∈[-1，2]，∃x0∈[-1，2]，使g（x1）=f（x0），则m的取值范围是______．
----In recent years, _____problem of global warming has become very serious.
----That’s right. People are facing _____diversity of natural disasters now.
A．/, a
B．a, the
C．the, a
D．a, a
