In caring for a client who is receiving linezolid IV for nosocomial pneumonia, which assessment finding is most important for the nurse to report to the healthcare provider?

A. Increased fatigue is a common side effect of many medications and illnesses but is not as immediately concerning.B. Watery diarrhea can indicate a serious side effect such as Clostridium difficile-associated diarrhea, which requires prompt medical attention.C. Nausea and headache are common side effects but are generally not urgent.D. Yellow-tinged sputum can indicate infection but is not as critical as the potential for a serious gastrointestinal issue.