In a controlled experiment,
a. a control group is compared with one or more experimental groups.
b. there are at least two variables.
c. all factors should be different.
d. a variable is not needed.

A. A control group is compared with one or more experimental groups.

Its either a) or b),wind and water erosion gradually widen the canyon

1) the mayans built pyramids just like the egyptians. the mayans also used hieroglyphics like them.2) power was passed down by family. for example, if the father dies, the son would be the next king.3)they both built pyramids for their structures.4)the main crop for the mayans was maize.5)they also grew manioc, beans,  squash,  amaranth, and chile peppers.