Physics
The bats can fly in the dark because

They generate flashes of light
They can see the objects in darkness
They generate ultrasonic sound waves
They have weak legs and are likely to be attacked by predators

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Physics
It is easier to roll a stone up a sloping road than to lift it vertical upwards because

Work done in rolling a stone is less than in lifting it.
Work done in lifting the stone is equal to rolling it.
Work done in both is same but the rate of doing work is less in rolling.
Work done in rolling is more than in lifting.

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