【单选题】先随机选择一些被访者并对其实施访问,再请他们提供另外一些属于所研究目标总体的调查对象,根据所形成的线索选择此后的调查对象,这是一种( )。
【单选题】If we were to allow that much current to go through the ignition switch, we would____ need a very large switch, but all the wireswould have to be the size of battery cables.
【单选题】If you need any article produced in this country, we shall be very glad to _______ for you.
【单选题】—Is the H1N1 flu (流感) very serious now? —No, I don't think so. However, we _______ need to be careful with it. [ ]
【单选题】当航空器要求空中放油时,航空器驾驶员应当通知管制单位。需要管制单位与航空器驾驶员进行协调,以下不正确的是
【单选题】At a time of this economic crisis, our _____ should be very clear about what we need to do.
【单选题】Although _______ manga (日本漫画) can be very interesting, we need to remember that _____ other kinds of things is necessary.
【简答题】柱塞式液压缸是( )式液压缸,液压油进入油缸时,推动柱塞带东运动部件移动,但( )退回时必须靠其他外力或自重来驱动。
【判断题】树种组成单一、林分结构简单是当前我国森林培育的问题之一 ( )