Find the synonym of the underlined word.
Many properties of the atmosphere affect the amount of solar radiation that reaches the earth.

• Concept: The meaning of the given word properties means a specific quality of a thing. So, the synonym of the given word properties are the choice D .characteristics.
•  Characteristics mean a plain feature of something. The word characteristics have the same aiming to the word properties. Therefore, the option D is that the correct option. 
• The word properties and characteristics are synonymous with one another.
  The given word within the option.
• Option A: belongings means an individual's movable possessions.
• Option B: The word impurities within the option b means a particle that impairs the standard of something.
• The word levels within the option c mean a grip on a scale of amount or quantity.
• The options A, B, C are incorrect because they are doing not have the similar meaning of the given option and don't seem to be the acceptable synonyms.
   

Hence, option D is the correct answer.