<p>The use of the conjunction “and” in the first choice is imprecise. So even if you were to fix the parallelism error as by writing:</p>
<p>Bats and mosquitoes come out at twilight, and the bats come to look for mosquitoes while the mosquitoes come to look for people.</p>
<p>the sentence would still be poorly written.</p>
<p>[By the way, why do you view the question as “weird”?]</p>