Supply the Missing Premise or Conclusion to Make a Properly

Multiple Choice

Supply the missing premise or conclusion to make a properly structured Argument from Principle.
1) A practice should be illegal if it encourages desperate people to do potentially harmful or degrading things
2) ) ..
So, prostitution should be illegal.

A) Prostitution is the oldest profession, and will be forever with us.
B) It doesn't make sense that prostitution is currently legal.
C) Potentially harmful professions should be illegal.
D) Prostitution is a practice that encourages desperate people to do potentially harmful or degrading things.