题型:填空题 — Why are you so late? I _____ for more than an hour. — I'm terribly sorry. I overslept and missed the bus.A. am waitingB. was waiting C. have been waiting D. will be waiting 查看答案
题型:填空题 — _____, Tom,Where's my doll? — Oh, sorry, I don't know. I think _____ behind the door. [ ]A. Excuse me, it's B. Here you are, she's C. I'm sorry, its D. How are you, he's 查看答案
题型:填空题 下面关于dBi、dBd、dBc、dB说法正确的是()A.dBi和dBd是考征增益的值(功率增益),两者都是一个度量单位B.dBi的参考基准为偶极子,dBd的参考基准为偶极子全方向性天线C.如果甲天线为12dBd,乙天线为14dBd,可以说甲比乙小2dBcD.dBc是一个表示功率相对值的单位,与dB的计算方法完全一样 查看答案