你好,这个and连接的是两个句子,and后面是一个省略的虚拟条件状语从句,还原就是if I had not did enough English reading before the exam,I could not achieve a so high score. 虚拟条件状语从句需要倒装,题目故意拆分成一个陈述句来误导你看清整个句子的中心,就成了I did enough English reading before the exam and (if)had I not,I might not have achieved a so high score. 译:如果我不曾在考试之前做足够多的英语阅读,我不可能得到一个如此高的分数。