Are you happy ______ your good friends here? [ ]
A. see
B. to see
C. seeing
D. sees
答案:B
2007的倒数是______,-2的绝对值是______.
对于每一功率级的最高功率控制级,一般测试条件下最大容限为±2dB,极端条件下的容限为±2.5dB。()