He . . . . . . that he could speak five languages.

The correct answer is boasted.

To boast is to talk about yourself in a way that shows that you are proud of yourself or your achievements. In this case, the man is boasting about his ability to speak five languages.

The other options are not as likely in this context.

• Challenged: To challenge someone is to ask them to do something difficult or dangerous. In this case, the man is not asking anyone to do anything, so he is not challenging them.
• Submitted: To submit something is to give it to someone in authority. In this case, the man is not giving anything to anyone in authority, so he is not submitting anything.
• Suggested: To suggest something is to say that you think it would be a good idea. In this case, the man is not saying that it would be a good idea for someone to speak five languages, so he is not suggesting anything.