Stars form from what celestial objects ?

  Stars are born within the clouds of dust and scattered throughout most galaxies. A familiar example, a dust cloud is the Orion Nebula. Turbulence deep within these clouds gives rise to knots with sufficient mass that the gas and dust can begin to collapse under its own gravitational attraction. Stars begin their lives as clouds of dust and gas called nebulae. The gravity of a passing star or the shock wave from a nearby supernova may cause the nebula to contract. Matter in the gas cloud will begin to coalesce into a dense region called a protostar.

b. the carbon cycle ensures living things have a source of hydrogen

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