报春花的花色白色(只含白色素)和黄色(含黄色锦葵色素)是一对相对性状，这对性状由两对等位基因(A和a,B和b)共同控制。显性基因A控制以白色素为前体物合成黄色锦葵色素的代谢过程；显性基因B可抑制显性基因A的表达，其生化机制如下图所示。请据此回答：

(1)开黄花的报春花植株的基因型可能是________，开白花的纯种植株的基因型可能是__________。

(2)通过图解可知：基因A和基因B是通过控制__________来控制代谢过程，从而实现对花色的控制的。

(3)为了培育出能稳定遗传的黄色品种，某同学用开纯种白花植株设计杂交育种方案如下：

①．选择基因型为___________________________的两个品种进行杂交获得F_1；

②．让F₁植株自交获得F₂；

③．从F₂植株中选择开黄花的个体进行自交留种；

④．重复步骤③若干代，直到后代不出现性状分离为止。

(4)根据上述实验，回答相关问题：

①．控制报春花花色遗传的两对基因是否遵循基因自由组合定律_________(填“是”或“否”)。

②．F₂中开黄花与白花的植株之比为_______________；开黄花的植株自交，后代中开黄花的纯合子占全部F₃植株的____________。

③．上述育种方案利用的原理是___________________。

One of the most widely used routing protocols in IP networks is the Routing Information Protocol(RIP)．RIP is the canonical example of a routing protocol built on the (71) algorithm．Routing protocols in internetworks differ slightly from the idealized graph model．In aninternetwork，the goal of the routers to forward packets to various (72) ．
Routers running RIP send their advertisement about cost every (73) seconds．A router also sends an update message whenever an update from another router causes it to change itsrouting table．
It is possible to use a range of different metrics or costs for the links in a routing protocol．RIP takes the simplest approach，with all link costs being equal (74) Thus it always tries tofind the minimum hop route．Valid distances are 1 through (75) ．This also limits RIP torunning on fairly small networks．

A．10
B．30
C．60
D．180