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The critical velocity of a liquid flowing through a tube is 

1. directly proportional to coefficient of viscosity
2. inversely proportional to density of the liquid
3. directly proportional to the radius of the tube
4. inversely proportional to the radius to the tube

Pauli's exclusion principle states that in an atom

When a particle moves in a circle with a uniform speed

What is the historical importance of September 11, 2001 ?

"Success does not mean the absence of failures"

Who said this ?