You can hear the sound of an approaching train long before you see it by placing your ear on metal track

Yes,

It is because the speed of sound in solids is very higher than speed of sound in gasses(air). As the molecules present in the solids are very close to each other and transfer disturbance easily and quickly to other molecules. In gasses molecules are farther apart and require more time to travel. Hence speed of sound in gasses are lower than in solids.

Second reason '

AS  velocity = V = square root [ elastic modulus /density ]

Gasses are more compressible and hence have smaller elastic modulus so have lower speed .

scientific laws are the result of testing theories and proving them to be facts.

it has to be b, about 97 percent.