Physics
The velocity of sound in air

Does not depend on temperature
Increases with decrease of temperature
Decreases with decrease of temperature
Decreases with increase of temperature

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Physics
When a piece of pure silicon is doped with aluminium, then

The doped silicon piece will become p-type
The resistivity of the doped silicon piece will increase
The conductivity of the doped silicon piece will remain the same
The doped silicon piece will become n-type

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Physics
Railway tracks are banked on curves

the train may not fly off in the opposite direction
necessary centrifugal force may be obtained from the horizontal component weight of the train
necessary centripetal force may be obtained from the horizontal component of the weight of the train
to avoid frictional force between the tracks and wheels

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