The correct answer is (c) 20-300 people
Explanation: Once the initial safety of the study drug has been confirmed in Phase I trials, Phase II trials are performed on larger groups 20-300 and are designed to assess how well the drug works, as well as to continue Phase I safety assessments in a larger group of volunteers and patients. Phase 1 trial will be done on 20-50 people. Phase 3 trial will be done on 300-3000 people. Phase 4 trial is post-marketing surveillance.