The answer is 15. Just count the spaces between A and D.
The law of detachment<span> allows you to "detach" the hypothesis from the conclusion. If we know both that </span>p<span> and </span>p<span> → </span>q<span> to be true, then we may conclude that </span>q<span> is true.
So the answers is the fourth one: I</span>f p <span>→</span><span> q is a true statement and p is true, then q is true.</span>
