Phase I clinical trials primarily involve:

• A. Phase I: tests the drug in a few people for safety and adverse reactions and determines safe and unsafe doses
• B. Phase I: tests efficacy in larger groups of people
• C. Phase I: determines long-term safety in the general population
• D. Phase I: compares the new drug to proven treatments

Answer: (A)

Phase I trials are all about safety and dosing in humans. They involve a small number of participants and focus on how the drug behaves in the body, what adverse effects may occur, and what dose levels are tolerable. The primary aim is to determine safe and unsafe doses and establish a starting point and escalation plan for further testing. This groundwork lets later studies assess whether the drug can be effective at doses that people can tolerate.

That’s why this option fits best: it describes testing in a few people for safety and adverse reactions and figuring out safe versus unsafe doses. The other statements describe goals of later phases or different purposes—evaluating efficacy in larger groups (Phase II/III), assessing long-term safety in the general population (larger, later studies), or comparing the new drug to standard treatments (usually Phase III). In oncology, Phase I might include patients rather than healthy volunteers, but the core aim remains safety and dose determination.