Lenses are made to have different focal points. What two properties of a lens affect the focal length?
A. Where the object is located
O B. Whether the image is virtual or real
O C. The material the lens is made from
O D. The centers of curvature of the two sides of the lens

african americans demonstrated their newly found freedom by relocating often in search of relatives whom they had been separated from during slavery. others established schools to educate freed people and they built institutions such as churches and political organizations to advocate for their rights.

the reaction mixture contains some ammonia, plus a lot of unreacted nitrogen and hydrogen. the mixture is cooled and compressed, causing the ammonia gas to condense into a liquid. the liquefied ammonia is separated and removed. the unreacted nitrogen and hydrogen are then recycled back into the reactor .