Movies, television, advertisements, and magazines have a tendency to portray thin women and muscular men. do you think this accurately portrays reality? how do you think this type of media affects the body image of america's youth? does thin necessarily mean fit or healthy? what other things influence body image?

You can write in slightly more detail but the simplest answers would be

1) No, this does not accurately portray reality (many different body shapes and sizes)
2) This media coverage ignores most body types to highlight the "ideal" body type and causes self-image issues with the American youth who do not see themselves represented on their favorite TV shows. 
3) No, thin is a description and does not imply fitness or health. (think about people who starve themselves or are starving and people who eat junk food but have high metabolisms)
4) Other things that influence body image are how people talk to you about your body, how you hear other people talking about their bodies if you see anyone with/out the same body type as you. Hearing negative things about your body from someone that you trust or value can hurt your self-esteem.