勾头螺栓用于钢模板与内外钢楞的加固，安装间距一般不大于（）mm，长度与采用的钢楞尺寸相适应。

A.300

B.600

C.500

D.1000

Most IP layer-based proxy mechanisms, such as network address translation (NAT), only support uni-directional proxy, from the internal network to external network (the Internet). The proxy establishes the communication channel by (66) IP addresses. The IP addresses must be (67) . 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 (68) for each application that uses (69) channels. SOCKS identifies communication targets through domain names, overcoming the restriction of using private IP addresses. SOCKS can use domain names to establish communication between separate LANs, with (70) IP addresses.

A．plenty

B．many

C．multiple

D．more