读图，回答1－2题。

1．图中①、②、③、④代表黄赤交角的是：[ ]

A．①

B．②

C．③

D．④

2．与图中β角的数值相等的纬线是：

[      ]

A．南北回归线

B．赤道

C．南北极圈

D．日界线

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 (86) IP addresses. The IP addresses must be (87) . 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 (88) for each application that uses (89) 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 (90) IP addresses.

（87）是（）

A.routable

B.locatable

C.path-selected

D.road-defined