Which Approach Would Be Most Helpful in Determining Whether the Gene

Which approach would be most helpful in determining whether the gene for a particular protein is the same length in frogs, humans, and trees?

A) use cDNA library construction and agarose gel electrophoresis
B) use genomic library construction and PCR
C) use DNA cloning and DNA hybridization
D) use PCR and agarose gel electrophoresis