I think the answer is D because of natural selection. The insects that survived had specific genes that made them resistant. They then passed those genes to their offspring and eventually the entire population was resistant. Hope this helps.
<h2><em>The trachea connects the larynx to the bronchi and allows air to pass through the neck and into the thorax. The rings of cartilage making up the trachea allow it to remain open to air at all times</em></h2>
