下列运算中，结果正确的是[ ]
A．x3·x3=x6
B．3x2+2x2=5x4
C．（x2）3=x5
D．（x+y）2=x2+y2
答案：A
Until the noise of the bus ________, we were able to hear the program again. [ ]
A. died from
B. died out
C. died away
D. died off
关于TCAS天线，下列说法正确的是（）。
A.由于TCAS测试时不测试天线，所以TCAS不会显示天线故障
B.TCAS天线是方向性天线，因为他有四个不同阻值的天线绕组
C.上下TCAS天线不能互换
D.以上说法都不正确
