Answer:Continue speaking about beetles
Explanation:
Autism is type of disorder in which a person tends to face difficulty while interacting and communicating with others and have repetitive behavior.
According to the situation described in question, David persists autism and has knowledge and interest in study that makes other amazed. If he is speaking about beetles for 20 minutes he will continue to speak further about them.
As he persist repetitive behavior he will continue his talking as he faces difficulty in interacting the other students even when they are bored from his speaking.