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
答案是e没有问题
笔记中对a的解释是，should it be that结构错误，应为：should test scores show that…should引起虚拟结构，正确的表达方式应为should sth do…
我的问题是，如果按照A，句子更正为

Several educational research groups are denouncing the mayor's proposal of a system by which individual teachers would be given raises or bonuses should test scores show that their students' mastery of reading skills has improved over a nine-month period.
should test scores show that…是做从句吗？individual teachers would be given raises or bonuses 是主句？