问个虚拟？

72.   (28395-!-item-!-188;#058&003974)

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

答案：E

破解解释 should引起虚拟，should sth do 是正确的结构，谁能讲解下这个结构,以前没遇到过

谢谢

这题的If子句应该纯粹是表条件的副词子句，虚拟应该是指假设语态，这题并没有牵涉到假设语态的成份在内

If的省略用法如下:

If S1+should/were/had→Should/Were/Had+S1

我是觉得(A), (B), (C)三选是if子句的省略型，但应该跟假设语态无关