立方得27的数是______；平方得9的数是______．
立方得27的数是 3；平方得9的数是±3．
故答案为：3；±3．
—Guess what, we've got our visas for a short-term visit to the UK this summer. —How nice! You（）a different culture then.
A. will be experiencing
B. have experienced
C. have been experiencing
D. will have experienced
振铃电路把交换机送来的（）交流电流变成直流电流，然后再产生两种不同频率的交替信号，驱动振铃器发出声音。
A.50Hz
B.60Hz
C.100Hz
D.25Hz
