Which One of the Following Statements Concerning Nephelometry Is Correct

Which one of the following statements concerning nephelometry is correct?

A) Nephelometry is the measure of the concentration of particles by measuring the amount of incident light blocked by the particles.
B) In a nephelometric measurement,light blocked by solutes in the solution at 180° from the incident light is measured by a photodetector.
C) The decrease in the intensity of scattered light is directly proportional to the number of particles in the solution,and the measurement of this decrease is called nephelometry.
D) In a nephelometric procedure,the measurement of scattered light that is not in the direct path of the transmitted light is made at right angles to the incident light.