参考答案:D
make contribution to doing sth. 意为“为……作贡献”,to在这里是介词,故其后用ing形式。故选D。
第39题: [单项选择]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.
参考答案:C
答案解析:Testicular enlargement signifies the onset of puberty in the male adolescent. Then sexual developmen
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