Answer:
I think It A
Explanation:
I read about it, so take your chance.
The circulatory system helps the excretory and digestive system do their jobs because the waste from the blood in the circulatory system is eliminated from the body through the excretory system, and the nutrients absorbed by the digestive system are transported through the blood.
A. Natural Selection. This is because the weeds that are not resistant to it die out before they can reproduce, but the resistant ones grow to maturity and then reproduce, passing down the resistance gene. Over time, the resistance gene would become a normal thing in weeds, while the non-resistant gene would not exist anyone, since the gene could not be passed on.