题目

It is reported that the United States uses _______ energy as the whole of Europe. A . as twice B . twice much C . twice much as D . twice as much 答案：D4．已知实数a，b满足0≤a≤1，0≤b≤1，则函数y=$\frac{1}{3}$x3-ax2+bx+c有极值的概率（　　）A．$\frac{1}{4}$B．$\frac{1}{3}$C．$\frac{1}{2}$D．$\frac{2}{3}$