Which is one cause of bullying? being a victim of physical abuse.
being well-connected to positive peers.
practicing tolerance of others.
having access to electronic technology.

The answer to your question would be:

A, being a victim of physical abuse.

Say you are getting abused by your parents daily, and you have no one to help you or any help at all. No ranting or venting. You would resort to other measures to relieve yourself, such as taking out your feelings on other.

Thus, causing bullying to occur.

Hope this helps you!