伊斯兰的信仰有几个层次？
参考答案：
三个层次：服从、信仰和行善。如果笼统地称呼时，任何一个层次都能代表伊斯兰的全部。
— There is no spare chair in the meeting room. Do you still need any?
— Yeah,I think four _____ chairs are needed for the lecture this afternoon. [ ]
A. dozen
B. dozens
C. dozen of
D. dozens of
5x（x2﹣2x+4）+x2（x+1）的计算结果是[ ]
A．6x3﹣10x2+20x
B．5x3﹣11x2+20x
C．6x3﹣9x2+20x
D．5x3﹣10x2+20x
