煤矿井下爆破炮眼深度小于（）时，不得装药、爆破。
A.0.4m
B.0.5m
C.0.6m
D.0.7m
参考答案：C
A．35°
B．70°
C．55°
D．110°
Creating world peace is a rather difficult goal, ____ calls for efforts of many generations.
A．one that
B．one
C．that
D．it
