Right answer is (d) Dew/fost point or Parts Per Million or Relative Humidity
Easy explanation: Most commonly units for humidity measurement are Relative Humidity(RH), DEW/Fost point (D/F PT) and Parts Per Million(PPM). RH is a function of temperature. DEW/Fost point is a function of the pressure of the as but is independent of temperature and is therefore defined as absolute humidity measurement of temperature. PPM is also an absolute measurement.