Babies that are at a low birth weight are more likely to have health problems, while women will have difficulty delivering babies with high birth weight. Together this leads to for babies of average birth weight. a. Stabilizing selection
b. Disruptive selection

That is

Afew buddies come over to your house to hang out. they notice you're struggling in school, perhaps you have to rely on to pass your class, but you can't absorb the knowledge. they could positively reinforce getting a tutor and working with you, dedicating more time to the areas of struggle and less on hanging out to better yourself.secondly, say you're the victim of bullying. you're afraid to tell an adult because of possible repercussions from the bully himself. your friends encouraging you and pushing you towards telling an adult for your safety is another example.