Why are mountians narrower at the top than at the bottom?

Atown is built on the banks of a small lake on the edge of a desert. after some time, the townspeople discover that water from the lake has become too polluted to use. describe one way that the lake may have been contaminated by the actions of the townspeople, and explain how the townspeople can remediate this problem.

#4.) describe the most likely weather conditions at indiana / ohio boarder. also could someone double check my other answers? i'd really appreciate it

In the diagram below dab and dac are adjacent angles