离心桶的装载、平衡、密封和打开必须在生物安全柜内进行。
参考答案：对
Packet-switching wireless networks are preferable (1) when transmissions are (2) bemuse of the way charges are (3) per packet. Circuit-switched networks are preferable for transferring large files or for other lengthy transmissions because customers are (4) for the (5) of time they use the network.
2（）
A．long
B．short
C．large
D．small
观察下列图片，联系所学知识，回答问题。
（1）它们的名称分别是什么？
