【单选题】China is famous ______ the Great Wall. [ ]
【单选题】China is famous _____ its tea. [ ]
【简答题】产生异方差的原因是什么?试举例说明经济现象中的异方差性。
【简答题】SPF猪是指没有()、()、()、()病原体。
【简答题】异方差产生的主要原因有哪些?举个例子说明经济现象中的异方差性。
【单选题】 Joe was caught in a traffic jam and when he got to the theatre, the play ________ for half an hour.
D.
had already been put on