Why is there hair on the underside of a leaf?

Because I am also looking for an answer for this but nobody wants to answer so i finally found the answer. But first, let me tell you about my day.Today, i ate a plate of chicken rice, go to tuition, did 30 queestions,go toilet,chat,wash hands,eat,another tuition,come home,eat,sitting here playing with the computer. So actually, i also need an answer because i also haven find out yet. So i cannot help you. OH, because butterflies have to protect their children.