单选题 Which of the following observations signals the onset of puberty in male adolescents?
A. Appearance of pubic hair.
B. Appearance of axillary hair.
C. Testicular enlargement.
D. Nocturnal emissions.

【正确答案】 C

【答案解析】Testicular enlargement signifies the onset of puberty in the male adolescent. Then sexual development progresses, causing the appearance of pubic hair and axillary hair and the onset of nocturnal emissions.