单项选择题

According to the passage, what may cause the periodic change of certain plants

A．It is caused by intensity of sunlight.
B．It is decided by humans' daily activities.
C．It is the result of chemical reactions by scientist.
D．It is up to the regular recycling of time.

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单项选择题

Which statement is true according to the passage

A．Human beings' activities may not be influenced by the shift of a day.
B．When you fall asleep at night, your temperature may lower to bottom point.
C．Human beings' hormones may keep a steady secretion amount all day longer.
D．If you sleep at daytime, your biological clock can operate better.