Why are vestigial structures not removed by natural selection?

what statement best describes the difference between the sympathetic and parasympathetic nervous systems?

the sympathetic nervous system prepares the body for intense physical activity and is often referred to as the fight-or-flight response. the parasympathetic nervous system has almost the exact opposite effect and relaxes the body and inhibits or slows many high energy functions.

sex cells are usually half's then they find another half and make a fertilize egg

the answer is d p: cell, q: organ, r: organ system, s: tissue