C. This is an old link from 1.5 years ago, but discusses the "Mars helicopter":

https://www. cnn. com/2018/05/12/us/mars helicopter/index. html

After the helicopter's solar cells charge its lithium-ion batteries, NASA controllers on Earth will prepare the craft for its tricky test flights.
To rise into the Mars'thin atmosphere, the helicopter's two counter-rotating blades will turn at nearly 3,000 revolutions per minute, or more than 10 times as fast as a helicopter's blades on
Earth, NASA says.
"The altitude record for a helicopter flying here on Earth is about 40,000 feet. The atmosphere of Mars is only 1% that of Earth, so when our helicopter is on the Martian surface, it's already at
the Earth equivalent of 100,000 feet up," Mimi Aung, the Mars Helicopter project manager at NASA's Jet Propulsion Laboratory, said in a news release.

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