Answer:
Sentence #1
Step-by-step explanation:
The sentence that contains an error in pronoun use is sentence number 1 - "Marcus and his brothers always help his dad with maintaining the lawn every weekend." The pronoun "his" in this sentence is referring to Marcus, but it should refer to Marcus's dad.
To correct the sentence, it should be written as "Marcus and his brothers always help their dad with maintaining the lawn every weekend." The possessive pronoun "their" correctly refers to the dad, indicating that the lawn belongs to him.