a. He only knows he should be looking for an Athenian.
Explanation:
The main reason why Puck makes a mistake with the love potion is because he is not given enough instructions. Puck is told that he is to use the magic potion on an Athenian man who is being pursued by a lady. These are Demetrius and Helena. However, he is unable to find them. Eventually, he comes across Lysander and Hermia, another Athenian couple. The two are sleeping separately, which leads Puck to assume them to be the two youths mentioned by Oberon.
