在无法考察总体时，要从总体中抽取能代表总体的样本作为考查对象。()

未分类题Whats the reason for the decrease of the number of illegal immigrants?A．The political and social disorder in the U. S.B．American's struggling economy and the increased enforcement of immigration laws.C．Their unwillingness to do low-skilled jobs.D．The increased return migration.

未分类题The word 'cinch'(Line3, Para.1)most probably meansA．a very easy thing.B．a very complex thing.C．a great challenge.D．an extremely hard problem.

判断题数据的存储结构是数据的逻辑结构在计算机存储器上的实现，它是依赖于计算机的。()

单项选择题绝对优势理论的主要代表人物是()A、亚当.斯密B、大卫·李嘉图C、里昂惕夫D、保罗·萨缪尔森

未分类题It can be inferred from the second paragraph thatA．low-altitude clouds are the main causes of global warming.B．increase of cloud cover can slow down the climate change.C．global warming will increase cloud cover.D．increase of cloud cover can speed up the global warming.