单项选择题

The main idea of the first paragraph is that ______.

A．people traveled on lakes thousands of years ago
B．people used logs thousands of years ago
C．traveling was hard thousands of years ago
D．there were no roads and cars thousands of years ago

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单项选择题

The main idea of the third paragraph is stated in the ______.

A．first sentence
B．second sentence
C．third sentence
D．last sentence

单项选择题

In total darkness, doves ______.

A．use landmarks
B．don't know which way to fly
C．fly back home
D．wait for the stars to appear