The appalachian mountains have been over time.
a.
eroding
b.
growing taller
c.
getting longer
d.
sinking into the ocean

The Appalachian Mountains have been eroding over time. The correct option among all the options that are given in the question is the first option or option "A". The Appalachian Mountain was similar in height to the Alps before it eroded. I hope the answer helps you.

This is all you, but i can give you some topics that you could try. if it rained when you want to do something outdoors, it 'limits' that human activity. maybe you want to do an experiment that goes throughout the whole year and you have to have above freezing the entire year. this 'limits' your activity. i thought of those just off of the top of my head. something that gets to me that might be getting to you is you are thinking too hard about what to do. think simply, and if it is too simple, then bump it up just a little bit.