Question

ppm stands for:
parts per megawatt
parts per milligram
parts per milliliter
parts per million

Explanation:

PPM is an abbreviation for "parts per million", a common unit used to express very low concentrations of substances in mixtures, widely applied in fields like chemistry, environmental science, and engineering. The other options use incorrect suffixes that do not match the standard definition of PPM.

Answer:

D. parts per million