简述在什么情况下不得进行高空作业。
参考答案：风力在六级以上、大雾、大雪和雷电等天气禁止高空作业。
The great achievements in recent 30 years have proved that the reform and open policy is a vital measure that ________ the national conditions of China.
A．fits into
B．turn into
C．break into
D．look into
下列图示变化为吸热反应的是
