Biography is the study of:

Biography is fundamentally the study of an individual's life. It involves chronicling significant events, relationships, achievements, and challenges to provide a comprehensive understanding of a person's journey. Therefore, "Lives of people" is the accurate answer. Option A, "Plants," is the domain of botany. Option B, "Maps," falls under cartography. Option C, "Rocks," is the subject of geology. Each of these distractors represents distinct fields of study unrelated to the personal histories that biographies explore.