在图中，能正确表示小磁针静止时N极指向的是 （ ）
答案：C
小磁针静止时N极指磁场方向，A图向右，B图向左，C图向左，D图向右，故C对。
可以降低血糖的激素有（）
A．胰岛素
B．胰高血糖素
C．胰岛素样生长因子
D．生长激素
E．生长激素释放抑制素
Frame Relay is simplified form of (71) ,similar in principle to (72) , in which synchronous, frames of data are routed to different destinations depending on header information. Packets are routed throught one or more Virtual Circuits known as (73) . Most Virtual Circuits are (74) ,which means that the network provider sets up all DLCI connections at subscription time. (75) are also part of the Frame Relay specification. They privide a link that only lasts only as long as the session.
A．X.21
B．X.25
C．X.28
D．X.29
