Hello!
B - high school drop-outs would likely benefit the most if illegal immigration did not exist in the U.S.
Due to the fact that illegal immigrants are not legally in the country, they cannot obtain a driver's license/ID or any other legal documents. Most jobs require an ID when hiring. Because of this, illegal immigrants are forced to find low-paying jobs that to not ask for identification when hiring employees. Unfortunately, this puts legal American high school drop-outs at a disadvantage. Drop-outs do not have the chance to earn a diploma or any high-level credentials. This means that they would also need the low-paying jobs that the illegal immigrants are often working in. If illegal immigration did not exist in the U.S., high school drop-outs would benefit because they would be given the jobs that the illegal immigrants currently have.
I hope this helps you! Have a great day!