Given a scientific passage and an answer, generate a question for the given answer.
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Question: Passage: Descriptive statistics and graphs help organize data so patterns and trends are more apparent. Descriptive statistics include the mean and range. Types of graphs include bar, circle, and line graphs. Answer: graphs

Answer: Bar, circle, and line are all types of what?

Question: Passage: Chlamydia is the most common bacterial STI in the U. S. Females are more likely to develop it than males. Symptoms may include burning during urination and a discharge from the vagina or penis. Answer: chlamydia

Answer: What is the most common bacterial sti in the u. s.?

Question: Passage: Like mollusks and annelids, aquatic arthropods may have gills to exchange gases with the water (discussed below). Terrestrial arthropods, on the other hand, have special respiratory structures to exchange gases with the air. These are described in Figure below . Answer: gills

Answer:
What do aquatic arthropods use to exchange gases with the water?