求解一道语法题的做题思路以及知识点

ALEXLOVELIFE

Several educational research groups are denouncing the mayor's proposal of a system by which individual teachers would be given raises or bonuses should it be that test scores show their students' mastery of reading skills having improved over a nine-month period.

A.should it be that test scores show their students' mastery of reading skills having  
B.should it be that test scores show their students' mastery of reading skills have  
C.should test scores showing their students' mastery of reading skills has
D.if test scores showing their students' mastery of reading skills having  
E.if test scores show that their students' mastery of reading skills has

这题答案是D，求大神告知这道语法题的做题思路以及知识点

ALEXLOVELIFE

在线求解答

ayoyoyo

答案应该是E

首先，show后面应该是个句子或者是个名词，根据未划线部分看只能是句子。that最好别省略，省略也不是绝对错。
所以AD不可能对。D里面用showing更是毫无由来。

其次，their students' mastery of reading skills是improve的主语，这个主语是单数。B错误。

然后是C，完全不知所云，should后面怎么doing又冒出来了。

最后，E清楚明白无错误。

这种题不知道有啥思路可言。。。。