功率单位瓦和dBm的换算：10w=（）dBm。
参考答案：40
如果函数f(x)＝ax2＋2x－3在区间(－∞，4)上是单调递增的，则实数a的取值范围是_______．
Many trees ________ along the streets every year. So the air is very fresh now.
A．plant
B．are planted
C．planted
D．were planted
