Formulating more than one possible interpretation of your friend's behavior will limit your ability to keep an open mind.
a. true
b. false

That statement is false

By definition, keeping an open mind mean leaving the possibilities to more than one possible interpretation.

So by formulating more than one possible interpretation, it will NOT limit our ability to keep an open mind

B is the correct answer, because the statement is false. 

If you're trying to understand what your friend did from multiple perspectives - you're basically keeping an open mind. This will help you later on - when you have more data as you will know what is more likely to be true.