The most reliable sign of sexual maturity in girls is:

 # The most reliable sign of sexual maturity in girls is:

A. Change in voice

B. Age at first menstruation

C. Appearance of pubic hairs

D. Breast development

The correct answer is B. Age at first menstruation.

An interesting phenomenon of the last 300 or 400 years, particularly the 20th century, has been a generalized increase in size of most individuals. There has also been a lowering in the age of sexual

maturation, so that children recently have grown faster and matured earlier than they did previously. Since 1900, in the United States the average height has increased 2 to 3 inches, and the average age of girls at first menstruation, the most reliable sign of sexual maturity, has decreased by more than 1 year. This “secular trend” toward more rapid growth and earlier maturation continued in most countries throughout the 20th century (e.g., the mean age in Poland in 1982 to 1984 was 13.2 years, and 12.8 years in 1992 to 1994) but seems to be leveling off in the developed countries at present. That still means that signs of sexual maturation now appear in many otherwise-normal girls much earlier than the previously accepted standard dates, which have not been updated to match the secular change.

Ref: Proffit 6th Edition.