In $2016,$ ?the hoverboard was a fad that swept the United States. The self $-$ balancing scooters were battery operated. By July $2016,$ ?there were $99$ ?incidents involving the battery packs overheating, sparking, smoking, catching fire, or exploding. The incidents involved two manufacturers who used battery packs from a single supplier. One of the remaining manufacturers that had no such incidents ran an ad with the following language: "Make sure when you hover that the name on your board is ours. With us $,$ ?safety comes first. Unlike our competitors, we make our own battery packs. We know they are safe." Which of the following is correct about the ad $?$

?a $.$ ?The ad is one that crosses an ethical line in terms of representations about competitors.

?b $.$ ?The ad is defamatory.

?c $.$ ?The ad $,$ ?while harmful to competitors, is factual and not defamatory.

?d $.$ ?None of these are correct.