How to understand what exactly does not comply with Google Play policy?

Question

Google Play

After I submitted my application to Google Play for consideration, after five days I received an answer to the mail.

How to understand what exactly they do not like?

Hi Developers at NAME,
After a recent review, we found that your app NAME is not compliant with one or more of our Developer Program Policies. See below for more information about your app's status and how to correct the issue.
Reasons of violation
Issue with your app
Your app contains content that doesn't comply with the Unauthorized Use of Copyrighted Content policy.

Reasons for violation
About Unauthorized Use of Copyrighted Content policy
We don't allow apps that infringe copyright. Modifying copyrighted content may still lead to a violation. Developers may be required to provide evidence of their rights to use copyrighted content.
Publishing Status
App status: Rejected
Your app has been rejected and wasn't published due to this policy issue. If you submitted an update, the previous version of your app is still available on Google Play.

Answer 1

Did you use other people's materials? Music, sounds, images from the internet...