The error is in part (B), where "beside" should be replaced with "because" or "as" to make the sentence grammatically correct.
"Beside" is a preposition meaning "next to" or "by the side of," but in this context, it doesn’t make sense.
The sentence is expressing a reason for not being hungry, and the correct conjunction to use is "because" or "as" to link the clauses.
The rest of the sentence is grammatically correct. Conclusion:
The error is in part (B), where "beside" should be changed to "because" or "as."