The correct answer here is "in the air". This phrase acts as an adverb of place as it describes where the virus is located. These phrases can modify a verb, adverb and adjectives and tells us more information about them like in this example "where" something is. They can also tell us about "how" or "when" or "why".
C and D are the correct answers.
Backache backbeats backbench ... and so on if this helps your question
