My pencil is ________.[ ]
A. brokes
B. broken
C. brokening
D. brokened
答案：B
20.There used__________a post office at the corner of the street.
A．to be
B．to being
C．to have
D．to having
岩石抗压强度值的离散系数越大，说明岩石抗压强度平均值的可信度越高。
