螺旋桨的缺陷主要发生在（）上。
A．桨毂
B．桨叶
C．与尾轴的连接
D．锥孔
参考答案：B
历史上称唐玄宗统治前期为[ ]
A、文景之治
B、开皇之治
C、开元盛世
D、贞观之治
The world's population has grown _____ it was in 1800.[ ]
A. six times more than what
B. more than six times what
C. six times more than which
D. more than six times that
