2, black hair does not know how to study hard early, Bai Shoufang regrets studying late. From Yan Zhenqing's Persuasion.
3, teenagers are eager to learn, and an inch of time is not light. I didn't feel the dream of spring grass in the pond, and it was autumn before walking on the steps. -from Zhu's "Accidental Success"
4 black hair doesn't know how to study hard early, but it's too late to learn.
Flowers will reopen one day, and people are no longer young.
I wish you progress in your study O(∩_∩)O ha!
If it helps you, I still hope to adopt O(∩_∩)O!
If you still don't understand, you can continue to ask \ (o)/~