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: 
Chlamydia is the most common STI in the United States. As shown in the graph in Figure below , females are much more likely than males to develop chlamydia. Like most STIs, rates of chlamydia are highest in teens and young adults.


Question: Which  is the most common sti (sexually transmitted infection) in the united states?
chlamydia
Chlamydia.