鲫鱼的体形为梭形，这种流线型的好处是（  ）。

A．美观大方

B．利于克服运动时水的阻力

C．有利于隐蔽

D．有利于生殖

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．groups

B．blocks

C．models

D．modules