若a的值使得x2+4x+a=(x+2)2-1成立,则a的值为( )
A.5
B.4
C.3
D.2
∵(x+2)2-1=x2+4x+4-1=x2+4x+3,
∴a的值为3.
故选C.
Having finished lunch, the case was discussed.
A.they discussed the case
B.they had discussed the case
C.the case was discussed
D.the case had been discussed
无线局域网通常由以下哪些设备组成______。 Ⅰ.无线网卡 Ⅱ.无线接入点 Ⅲ.以太网交换机 Ⅳ.计算机
A.Ⅰ、Ⅱ和Ⅲ
B.Ⅱ、Ⅲ和Ⅳ
C.Ⅰ、Ⅱ和Ⅳ
D.Ⅰ、Ⅲ和Ⅳ