Urban land is the land that makes up a city or town. These maps show how the land use in Baltimore, Maryland, changed from 1966 to 1992. The level of pollution in this region also rose during this period.

Why do some dna fragments move farther than others during gel electrophoresis? a. because their shapes are different b. because they are different types of molecules c. because the samples are different colors d. because their masses are different