患者男性，75岁。股骨头骨折行股骨头置换术，术后卧床2周出现左小腿腓肠肌疼痛和肿胀，

一个质量为7.9g的实心铁球，先后放入盛有水银和水的容器中，当小球静止时，小球所受的浮力分别是多大？（ρ_铁=7.9×10³kg/m³，ρ_水银=13.6×10³kg/m³，g=10N/kg）

平垫密封的特点有哪些？

Most IP layer-based proxy mechanisms，such as network address translation (NAT)，only supportuni-directional proxy，from the internal network to external network(the Interned．The proxvestablishes the communication channel by (71) IP addresses．The IP addresses must be (72) ．These proxy mechanisms prevent applications that must establish return data channels from establishing their data channels，such as，multimedia applications．IP layer-based proxy mechanisms need additional software (73) for each application that uses (74) channels． SOCKS identifies communication targets through domain names，overcoming the restriction of Usina private IP addresses．SOCKS can use domain names to establish communication between separate LANs，with (75) IP addresses．

A．manufacturing

B．manipulating

C．conduct

D．implement

报告测量不确定度有二种方式，在进行基础计量学研究和基本物理常量的测量时，通常使用( )。

A．扩展不确定度

B．合成标准不确定度

C．A类不确定度

D．B类不确定度

当（）时会导致压缩机密封油槽液面的升高。

A.油槽压力低

B.仪表风中断

C.密封N₂压力高

D.压缩机漏油严重