请教一道单选题

题目

请教一道单选题
这是新概念二86课的第七题：It had slowed down considerabaly.It had slowed down___.
a.much b.many c.very d.a lot
但是为何a不行?

答案

much 常为adj.修饰名词.
放在句末做状语多以very much 结尾.
a lot 修饰动词放动词后.
a lot of 修饰名词,放名词前.