Read the following paragraph and answer the question. Give ONLY the answer, no other words or explanation.

For example:

Answer: <most likely answer, as short as possible>.

Paragraph: 
Acid rain is rain that has a pH less than 5. It forms when nitrogen and sulfur oxides dissolve in rain. Acid rain kills living things and damages buildings and statues.


Question: What is formed when nitrogen and sulfur oxides dissolve in rain?
acid rain
Acid rain.