Question

One study in america found that student's grades (improve) a little after the school interduced

One study in america found that student's grades (improve) a little after the school interduced uniforms.为什么不能用完成时

Answer 1

综述：现在完成时态不能与表示过去的时间状语连用，根据 after the school introduced uniforms可知 答案是用一般过去时态，improved。

重点词汇：improved

英［ɪm＇pru：vd］

释义：

adj.改良的；改进过的

v.改进；增加（improve的过去式和过去分词）；变得更好

短语：

Improved Calculator改良的计算器；改良的计较器；改进的盘算器；改进的计算器

例句

用作形容词（adj.）

Improved wheats will be introduced on a wide scale this year.

今年将大范围的推广小麦的改良品种。

The improved lid of this jar makes for easier opening .

这个改良过的大口瓶盖子易于开启。

Answer 2

主句的谓语动词found是过去式，that引起的宾语从句中一定用相应的过去时态，现在宾语从句中还含有一个时间状语从句after the school introduced the uniforms，表明学生成绩提高是在之后而不是之前，所以不能用过去完成时态。

Answer 3

One study in america found that student's grades improve a little after the school interduced uniforms.

that student's grades improve a little 用一般现在时宾语从句描述了一个事实所以用一般现在时。after the school interduced uniforms时间状语为that student's grades improve a little 服务，大致理解先introduce---后improve---，没必要用完成时态。

Answer 4

现在完成时态不能与表示过去的时间状语连用
根据 after the school introduced uniforms
可知 答案是用一般过去时态， improved
即

One study in America found that student's grades improved a little after the school introduced uniforms.

Answer 5

因为有表示时间顺序的连词after，说明动作发生的先后顺序。用一般过去时，不用过去完成时。

追答

这样的连词还有when,before