Dear KB:

You wrote:
>
> I have a promotion exam at work coming up. I am looking for an
> answer as to what is best to study in preparing for this test. The
> following is a sample question of what I will be looking at on this exam:
>
> Directions: Read the information given, and then select the choice which
> presents the information most clearly and accurately.
>
> Frank met Sam after the class. Sam received a call. Because of this,
> Frank left early.
>
> Which choice below presents this information most clearly and accurately?
>
> A. Frank met Sam after the class, but he left early because Sam received
> a call.
> B. Frank met Sam after the class, but he left early because he received a
> call.
> C. Frank met Sam after the class, but Sam received a call, so he left
> early.
> D Sam received a call when Frank met him after the class, so he left
> early.
>
> Explanation: Choice B sounds as if it was Frank who received the call.
> Choices C and D sound as if it was Sam who left early. Choice A makes it
> clear that Sam recieved a call and that Frank left early. Choice A is the
> BEST ANSWER because it is the only choice that is clear and accurate.
>
> -thank you
>
Sounds good. This is what we call an ambiguous antecedent problem. If the reader does not know for sure what person, place, or thing that a pronoun is referring to, then you have not communicated clearly.

For more on this see https://englishplus.com/grammar/00000030.htm.