(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
