many a，“单数”的“许多”

【问】

I’ve told you many ____ time not to ride your bike on the pavement.

答案：a

问题：many后为什么用a？ 

【答】

many a是固定搭配，意为“许多”，但形式是单数，做主语时，按“单数”搭配谓语动词，如：

• Many a good man has been destroyed by drink. 许多好人都毁在了饮酒上。
• Many a mother tries to act out her unrealized dreams through her daughter. 许多母亲都试图通过女儿实现她们未能实现的梦想。