过一点只能画出一条直线与已知直线垂直。[ ]
正确
Playing tricks on others is _____ we should never do. [ ]
A. anything
B. something
C. everything
D. nothing
青藏地区最突出的自然环境特征是：[ ]
A．干旱
B．湿润
C．高寒
D．寒冷
