多谐振荡器主要用来产生()。
参考答案:矩形波
We _____ what gift we should send to our teacher when Todd came up with a good idea. [ ]
A. argued about
B. had argued about
C. were arguing about
D. would argue about
对一国的政治风险进行评估的方法有许多种,其中依赖于专家力量的评估方法是( )
A.实地考察法和专家咨询法
B.专家咨询法和数量分析法
C.数量分析法和德尔菲法
D.专家咨询法和德尔菲法