问题
单项选择题
A．Melatonin is the source of a big push from biology that makes teenagers night owls.
B．Melatonin is a simple signal that turns on in the morning and turns off in the evening.
C．Melatonin is secreted several hours later in childhood than it will be during adolescence.
D．Melatonin doesn’t shut off until 11 o’clock P.M. every day.
答案
参考答案：A
解析：[听力原文]
Which of the following statements is TRUE about melatonin