The sequence of a dna fragment can be determined by observing the of fluorescent bands on an electrophoresis gel.
a. mass
c. temperatures
b. density
d. colors

A gel electrophoresis is used for separation of DNA (or RNA or proteins) or its fragments based on either size (mass) or charge. An electrophoresis gel can be stained in different ways. Whatever the staining is chosen, all of the fragments will glow the same color no matter what is the kind of fragments. Density and temperature cannot be determined on an electrophoresis gel.