制冷系统灌氨必须在制冷系统气密性试验和制冷设备及管道隔热工程完成并经检验合格后进行。
参考答案：对
单词拼写。
1. Science, according to Hawing, is often _______(误解).
2. I have a lot of _______ (困难)finding your house.
3. There are three pieces of _______ (家具)in the room.
4. A plan began to _________ (形成)in his mind.
5. I am sure they won't feel ________ (失望的).
由于试剂不纯引起的误差是( )。
A．偶然误差
B．系统误差
C．过失误差
D．或然误差
