设有: int a[4][5];则数组a占用的内存字节数是（ ）

A. 9
B. 20
C. 40
D. 80

以下程序的输出结果是（ ）#includeint main(){int i,a[3][3]={1,2,3,4,5,6,7,8,9};for (i=0;i<3;i++)printf(“%d,”,a[i][2-i]);return 0;}

A. 1,5,9
B. 1,4,7
C. 3,5,7
D. 3,6,9

指出以下错误语句（ ）

A. int a[2][3]={{1,2,3},{4,5,6}};
B. int b[2][3]={1,2,3,4,5,6};
C. int a[][]={{1,2,3},{4,5,6}};
D. int a[][3]={{1,2,3},{4,5,6}};

用带连接的通信指令实现PLC1（客户端）发送1个字节的数据0X21，PLC2（服务器端）接收PLC1发送过来的数据点亮1个LED。

It _______ (be) very late whenshe gets home, and her parents ________ (wonder) what’s happened.

A. is going to be, is going to wonder
B. will be, willwonder
C. is going to be,will wonder
D. will be, will be wondering

This time next month the snow______ (melt) and skiing _____ (be) over.

A. will melt, will be
B. will be melting, will be
C. will melt, is going to be
D. will be melting,is going to be

IPv4地址是?

A. 24位
B. 32位
C. 64位
D. 48位

下列是C类IP地址的是?

A. 192.168.0.1
B. 10.0.0.1
C. 168.1.1.1
D. 225.168.0.1

B类地址的子网掩码是?

A. 255.0.0.0
B. 255.255.0.0
C. 255.255.255.0
D. 255.255.255.255

双绞线线缆中共有几根线?

A. 4
B. 6
C. 8
D. 10