A:better educate
B:receive well educatio
C:better educated
D:accept better educatio
已知函数f(x)=﹣x3+ax2﹣x﹣1在(﹣∞,+∞)上是单调函数,则实数a的取值范围是( )
关于自然光和偏振光 ,下列观点正确的是( )
用如图所示装置来探究“观察水的沸腾”实验:
What the forest of the USA in the last 350 years?