Why don't humans need to carry out photosynthesis

Just reword this in your own way: In a Nutshell : We can't photosynthesize because we don't have chloroplasts, and we wouldn't get enough food out of it to make it worthwhile anyway.

Because we already know everything but our brain needed to see it to remember  it but we think we just found out about when we already knew it but we need to see it

Explanation:

its like this, "if i give a plant an unlimited amount of sunlight,then the plant will grow to its largest possible size."

hope it let me know if it does or doesn't =^-^=

substitution is the answer in this case