安全阀应经常保持清洁，防止被油垢脏物所粘满或锈蚀，随时检查铅封是否完好，温度过低时有无冻结的可能，安全阀是否有跑冒滴漏。
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安全阀一般至少每年检验一次，检验内容包括：清洗、研磨、零件更换、定压和气密试验。安全阀的定压值不得随意变更，其值最大不得超过容器的设计压力。69
A. 正确
B. 错误
关于热疗常见的不良反应，正确的是（）。
A. 浅部和深部热疗均易造成皮下组织坏死
B. 浅部热疗易造成皮下组织坏死，深部热疗易造成皮肤烫伤
C. 浅部热疗易造成皮肤烫伤，深部热疗易造成皮下脂肪硬结
D. 浅部热疗易造成皮下脂肪硬结，深部热疗易造成皮肤烫伤
How does a DHCP server dynamically assign IP addresses to hosts?（）
Addresses are permanently assigned so that the host uses the same address at all times.
B. Addresses are assigned for a fixed period of time. At the end of the period, a new request for an address must be made, and another address is then assigned.
C. Addresses are leased to hosts. A host will usually keep the same address by periodically contacting the DHCP server to renew the lease.
D. Addresses are allocated after a negotiation between the server and the host to determine the length of the agreement.
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