A:shouldn't have gone
B:mustn't have gone
C:couldn't have gone
D:mightn't have gone
一艘轮船在小岛A的北偏东60°距小岛80海里的B处,沿正西方向航行2小时后到达小岛的北偏西45°的C处,则该船行驶的速度为____海里/小时.
若不等式|x﹣1|<a成立的充分条件是0<x<4,则实数a的取值范围是____