The first and most obvious sign of precocious puberty in a 7-year-old female is:

Rationale: A. Pubarche (development of pubic hair) may occur, but it is not usually the first sign in girls. B. Leukorrhea (vaginal discharge) can appear later but is not the initial sign of puberty. C. Rapid onset acne may accompany puberty but is not the earliest or most obvious sign. D. Breast enlargement (thelarche) is typically the first and most noticeable sign of precocious puberty in girls.