This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: CLINICAL TRIALS, DRUG LABEL, Subject name: Pharmacology
Approximate number of patients recruited in phase II clinical trials of a drug are? 
Select and explain. 
A. 20-100, B. 100-500, C. 500-1000, D. 1000-5000
A: 20-100
Answer: A: 20-100 
Explanation: Phase Name Conducted on I Human Pharmacology and safety Healthy Volunteers II Therapeutic Exploratory (20-200) patients III Therapeutic Confirmatory Upto 5000 patients from several centres IV Post-Marketing Surveillance Large number of patients 0 (ZERO) Microdosing studies Healthy volunteers (Small numbers)