This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Other topics and Adverse effects, Subject name: Pharmacology
Define sustained fever? 
Select and explain. 
A. Fever is persistent and does not vary by more than 0.5degC/day, B. Fever is persistent and varies by more than 0.5degC/day., C. Fever is persistent and does not vary by more than 1degC/day, D. fever is persistent and varies by more than 1degC/day.
A: Fever is persistent and does not vary by more than 0.5degC/day
Answer: A: Fever is persistent and does not vary by more than 0.5degC/day 
Explanation: Sustained fever is persistent and does not vary by more than 0.5degC (0.9degF)/day. Remittent fever is persistent and varies by more than 0.5degC (0.9degF)/day. Relapsing fever is characterized by febrile periods that are separated by intervals of normal temperature; teian fever occurs on the 1st and 3rd days (malaria caused by Plasmodium vivax), and quaan fever occurs on the 1st and 4th days (malaria caused by Plasmodium malariae).Ref: Nelson; 20th edition; Chapter 176; Fever; Page no: 1278