Gel electrophoresis sorts dna strands by length because longer dna strands travel through the gel slower than shorter strands. why do scientists need to sort dna strands by length?

Gel Electrophoresis is a way to sort and measure the DNA strands. Scientists use the technique whenever they need to sort DNA strands according to lengths, this is because it helps them determine patterns, banding patterns create unique fingerprint for a certain individual. During the process the shorter strands move faster because they have less mass compared to the longer strand. Therefore, the short strands end up farther away from the starting point than the longer strands, which is how the different in lengths sort themselves out. 

The answer would be a. aluminum can

Cuz i said so. which gives it to b