How Can a Gene That Contains Introns Be Made Shorter

Multiple Choice

How can a gene that contains introns be made shorter (but remain functional) for genetic engineering purposes?

A) using a restriction enzyme (endonuclease) to cut the gene into shorter pieces
B) using reverse transcriptase to reconstruct the gene from its mRNA
C) using DNA polymerase to reconstruct the gene from its polypeptide product
D) using DNA ligase to put together fragments of the DNA that code for a particular polypeptide