Physics
An aircraft can perform aerobatic manoeuvres in a vertical loop because of

Gravity
Centripetal force
Weight
Centrifugal force

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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
On a clean glass plate a drop of water spreads to form a thin layer whereas a drop of mercury remains almost spherical because:

mercury is a metal.
cohesion of mercury is greater than its adhesion with glass.
cohesion of water is greater than its adhesion with glass.
density of mercury is greater than that of water.

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