D. all of the above would be your answer!
<span>When a river overflows its banks, it deposits sediment over a broad, flat area of land on both sides of the river. This broad flat area is called a floodplain. Floodplains usually have </span><span>areas of higher elevation on both sides</span>
C is the answer 3 + 2 +8 = 13
Sorry this will probably be pretty long.
So think of the "control" as being something you yourself add to increase or decrease the effects in an experiment.
I'll give you an example so it is not as confusing.
Say you have decided to make an experiment on plants. Which plant can grow the fastest on which type of liquid? What is being added to this experiment? The liquid! Or all of the liquids you used. Like if you used Coke, Lime Gatorade, Orange Gatorade, and Water. Each drink will EFFECT each plant differently.
Hope I was of any hope?
