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

Rationale:
A. In a healthy 10-year-old, a heart rate of 60 beats per minute at rest is concerning because the normal resting heart rate for this age group ranges from approximately 70–120 bpm. A heart rate below 70 bpm (bradycardia) may indicate an underlying cardiac conduction issue or other pathology, particularly if symptomatic.
B. 73 bpm is within the normal range for a 10-year-old at rest.
C. 100 bpm is normal and can be expected depending on activity, anxiety, or mild stress.
D. 120 bpm is at the upper limit of normal for a 10-year-old and may be appropriate depending on recent activity or emotional state.

Rationale:
A. Pulmonary valve stenosis typically produces a systolic murmur and thrill at the upper left sternal border.
B. A thrill palpated in the right clavicular region or upper right sternal border suggests aortic valve stenosis, as turbulent blood flow across a narrowed aortic valve produces a palpable vibration in this area.
C. Tetralogy of Fallot is characterized by a harsh systolic murmur at the left upper sternal border due to right ventricular outflow obstruction and does not typically produce a thrill at the right upper sternal border.
D. A ventricular septal defect generally produces a systolic murmur and thrill at the lower left sternal border, not the right upper sternal border.