安装GPS天线的地点要求视野开阔,GPS天线可以锁定()颗以上GPS卫星。
A.2
B.3
C.4
D.5
参考答案:C
有机物A可以发生下列反应:已知C能发生银镜反应,E不发生银镜反应。则A的可能结构有
A.1种
B.2种
C.3种
D.4种
— What ________ it be?
— It can't be a mail box, for it's moving. It ________ be a car. [ ]
A. must; must
B. can; can
C. can; must
D. must; can