A、Walking on the Moon is more difficult. B、Mars has less gravity than Moon does. C、People can’t keep balance on Mars. D、People n

　　Located at the NASA Research Center in Iowa is a 5 000-gallon vat of water. Inside the tank is an underwater running machine designed by Dava Newman, an aerospace engineer. (20) For four years Newman observed scuba divers as they simulated walking on the Moon and on Mars on her underwater moving belt. She wanted to discover how the gravity of the Moon and of Mars would affect human movement. To do this, Newman attached weights to the divers and then lowered them into the tank and onto the running machine. These weights were carefully adjusted so that the divers could experience underwater the gravity of the Moon and of Mars as they walked on the running machine. (21) Newman concluded that walking on Mars will probably be easier than walking on the Moon. The Moon has less gravity than Mars does, so at lunar gravity, the divers struggled to keep their balance and walked awkwardly. But at Martian gravity, the divers had greater traction and stability and could easily adjust to a pace of 1.5 miles per hour. As Newman gradually increased the speed of the running machine, the divers took longer, graceful strides until they comfortably settled into an even quicker pace. Newman also noted that at Martian gravity, the divers needed less oxygen. The data Newman collected will help in the future design of spacesuits for Mars. (22) Compared to lunar spacesuits, spacesuits for Mars will require smaller air tanks; and, to allow for freer movement, the elbow and knee areas of the spacesuits will also be altered.
　　20. What did Dava Newman do to find the effects of gravity on human movement?
　　21. What conclusion did Newman get?
　　22. What does the speaker say about the spacesuit for Mars?