Question

Yo___ con Teresa cuando el bebe empezo a llorar.

Answer 1

B Charlaba 
because when you used c and d you use them when you talk with more than 2 people.
A is when you use in the past and right now you are not talking in the past you are talking about the present because when you were talking the baby cried
Hope Ii had helped.

Answer 2

The answer is b, charlaba