The nurse is monitoring a client who has severe bone marrow suppression following antineoplastic drug therapy. Which is considered a principal early sign of infection?

The correct answer is C: Fever. Fever is considered a principal early sign of infection in a client with severe bone marrow suppression because it indicates the body's immune response to an infection. In this case, the client's compromised immune system due to bone marrow suppression makes them more susceptible to infections, and fever is one of the body's natural defense mechanisms to fight off infections. Tachycardia (A) and diaphoresis (D) can also be signs of infection, but fever is a more specific and reliable indicator in this context. Elevated white blood cells (B) may not be present in a client with bone marrow suppression.