Epithelial tissue helps cover your "exterior sources". Therefore I'm pretty sure the first one is Epithelial cells.
The Nervous System has to do with sense of feeling or sense of touch mostly. The Nervous System controls everything you do! ex. touching a table uses the nervous system.
The Skeletal System helps your body move and supports a lot of different things in your body. All of those other options are not correct just because they do not support. Here is what I mean in the shortest way possible:
