Answer: Option A is not completely correct because natural gas is categorized as a Newtonian fluid, but the viscosity of a Newtonian fluid is constant over time. Option B is not correct because unlike liquids, the viscosity of natural gas is increased by increasing the temperature. Option C is correct as the SI unit of viscosity is the Pascal second. Since 1 Pascal is equal to Newton m2 and 1 Newton is expressed as kg m s2 , then 1 Pascal is equal to kg ms2, and a Pascal second is equal to kg ms. Option D is not correct either since the unit of viscosity in CGS is dyns cm2 , equal to one poise. Thus, option C is correct.