What was a major cause of migration to the cities at the turn of the century

C. industrial jobs

Explanation:

I got it on Edmentum.

not concrete, existing in thought or as an idea but not having a physical or concrete existence

depends on your school

when i was in high school i took ap biology my senior year and it was the hardest one for me because my teacher finished the material within the first month of school and then went on to doing advanced college level it was horrible. but at a nearby school ap biology was one of the easier aps. also, it depends on what you are interested i like math a lot so ap calculus was easier for me than most but i hate history so ap us government was harder for me than most.