(二) 谓语动词的时态
①、主要考察时间状语

例 The metal aluminum has been first isolated early in the nineteenth century.
   A        B  C     D

分析:Metal, aluminum同位语,in the nineteenth century为明显表示过去时间的状语, 因此应该用过去时态,把has been改为was

②、For和since的区别
区别一:For 后面使用时间段,since 后面使用时间点
区别二:Since 只能用在现在完成时态,For 最主要用在现在完成时和一般过去时
  I has been a teacher for three years.
  I has been a teacher since 1996.
  I was a teacher for three years. 这种表达可以,for three years表示一段时间,was 表示过去做了三年,现在不是老师了

例: Since 1921 the budget of the United States became
   A      B             
  the primary responsibility of the president.
     C    D
分析:A错,应改 In. since一般要求主句用完成时态,而句中谓语动词为过去式,其时间状语应与之呼应,故改Since为In。

例:Adella Prentiss Hrghes served as manager of
             A  B  C  
  the Cleveland Orchestra since fifteen years.
            D
分析:D错,应改为for。since引导时间状语时,主句谓语动词为一般完成时;主句谓语动词为一般过去时要用介词for;而且一段时间用for, 而不是since。


52. In general, prawns lived in shallow coastal waters or in streams. 
   A       B        C     D
自然现象和客观事实用一般现在时态,live