Sentence four is representing the introductory phrase because it is describing why the main action has happened and how the main action has happened.
The main action is a car crashing through the front of Kayla's house that has happened because Jayla took her eyes off the road because Kayla called her.
After that, other sentences are explaining why the crash happened. It happened because one of the sisters was so worried that she had to call another one who was driving, and when she answered the call, she crashed her car because she took her eyes off the road.
