The Ozone Layer is part of Earth's Stratosphere.
Mexicans currently make up the largest portion of immigrants.
To put it shortly, the answers are C, D, E, and F.
With C. being "Increased Immigration",
D. being "The desire for adventure/land/riches",
E. being "The Discovery of gold", and
F. being "The Homestead Act".
Hope this helps :)
Hello!
Your answer is D. Gravity.
Hope this helps :))