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Given a scientific passage and an answer, generate a question for the given answer.

Passage: When current flows in just one direction, it is called direct current (DC) . The diagram below shows how direct current flows through a simple circuit. An example of direct current is the current that flows through a battery-powered flashlight. In addition to batteries, solar cells and fuel cells can also provide direct current. Answer: direct current
Output:
What kind of current flows in just one direction?