A、On and above the ground. B、Above the ground only. C、On or below the ground. D、Above or below the ground. D选项都是介词短语，是关于地点的。题目问的

In the United States, a company is working on a project that could change the way we think about public transportation. Its planned system would move people around in steel tubes. Those passengers would be traveling at speeds of up to 1,200 kilometers per hour. The futuristic steel tube transportation system is called Hyperloop. Workers plan to test the system next year in a specially built community called Quay Valley. The town will be powered entirely by energy from the sun.
    The Hyperloop transport system is the idea of businessman Elon Musk. Dirk Ahlborn is head of Hyper-loop Transportation Technologies. He says his company has taken Mr. Musk’s idea and is developing a system that will be safe, environmentally friendly and fast. ’’It’s 100 percent solar powered...we’re not going to get up to 760 miles per hour, but we believe we can actually break the records that are existing right now. ’’This means that a four-hour drive from Los Angeles, California to Las Vegas, Nevada, could someday take only 30 minutes by Hyperloop.
    The system involves a series of capsules that float inside a long tube. These containers would not need to travel along a pathway or track. The system has been designed to operate above or below ground. ’’Inside the tube you create a low pressure environment very similar to an airplane that’s at high altitudes. So now the capsule travelling inside the tube doesn’t encounter as much resistance, and therefore can travel really fast with very little energy. ’’
    Dick Ahlborn and his company will use an eight-kilometer track in Quay Valley to find the best way to set up passenger traffic and repair capsules. A larger system will cost an estimated six to $ 10 billion to build. If Mr. Ahlborn and his company succeed, we may one day see these very fast Hyperloop capsules speeding through tubes around the world.
20. What can we learn about Hyperloop?
21. What are the characteristics of Hyperloop?
22. Where has the system been designed to operate?