Given a scientific passage and an answer, generate a question for the given answer.
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Question: Passage: Dissolved mineral salts wash into the ocean. As ocean water evaporates, it leaves the salts behind. This makes the water saltier. Ocean water is about 3.5 percent salts. The main salt is sodium chloride. Answer: salts

Answer: Concentration of what, the substance left behind when ocean water evaporates, is about 3.5 percent?

Question: Passage: Cycloalkanes are hydrocarbons whose molecules are closed rings rather than straight or branched chains. A cyclic hydrocarbon is a hydrocarbon with a ring of carbon atoms. Answer: carbon atoms

Answer: Cycloalkanes are hydrocarbons whose molecules are closed rings rather than straight or branched chains. a cyclic hydrocarbon is a hydrocarbon with a ring of these?

Question: Passage: The digestive system is the body system that digests food mechanically and chemically and absorbs nutrients. The digestive system also eliminates solid food waste. The major organs of the digestive system include the mouth, esophagus, stomach, and small and large intestines. These organs make up the long tube called the gastrointestinal (GI) tract, which goes from the mouth to the anus. Answer: digestive system

Answer:
What is the body system that digests food mechanically and chemically and absorbs nutrients?