按要求写出下列符号． （1）2个水分子______；（2）钙离子______；（

有以下程序
main()
int n=0,m+1，X=2;
if(!n) X-=l;
if(m) X-=2;
if(X) X-=3；
printf("%d\n",x)；

执行后输出的结果是 【9】 。

甲容器中有浓度10%的盐水300千克，乙容器中有20%的盐水120千克，现往甲、乙两容器中倒入等量的水，使这两个容器中盐水的浓度一样，问要倒入多少千克水？

最简单的透镜两个表面都是球面的一部分，通过两个球心的直线，叫做透镜的 _________ ，如果透镜的厚度比球面的半径小许多，这种透镜又叫做 _________ ，其中心O点叫做透镜的 _________ ．

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 (1) algorithm．Routing protocols in internet works differ slightly from the idealized graph model．In an internet work，the goal of the routers to forward (2) to various networks．

Routers running RIP send their advertisement about cost every (3) seconds．A router also sends an update message whenever an update from another router causes it to change its routing table．

Routing protocols use different techniques for assigning (4) to individual networks．Further, each routing protocol forms a metric aggregation in a different way．RIP takes the simplest approach，with all link costs being equal (5) ．Thus it always tries to find the minimum hop route．Valid distances are 1 through 15．This also limits RIP to runing on fairly small networks．

3（）

A．10

B．30

C．60

D．180

根据《建设工程工程量清单计价规范》（GB50500--2013），实行工程量清单计价的工程，宜采用的合同类型是（）。

A.单价合同

B.总价合同

C.固定总价合同

D.成本加酬金合同