题目内容：

    Washing windows on a skyscraper is a dirty job. Hanging off the side of a building can also be dangerous, notes Oliver Nicholls, 19. So this 12th-grader invented a robot to handle the job.

Some recent incidents inspired his project. In one, a couple of high-rise window washers were standing on a platform that fell down. No one died, but the pair was seriously injured. Oliver also witnessed someone fall and break his leg while cleaning a glass awning (雨篷) over the entrance to a building.

The new robot is about the size of a medium-sized picnic cooler and weighs 12 to15 kilograms. It's designed to hang off the side of a building from ropes, just as current window－washing platforms do. A hose（软管）carries water to the robot. A cable (电缆) delivers it electric power. The computer controls the robot up-and-down movements by adjusting the ropes from which the robot hangs. When the robot needs to move from one window to another, a set of propellers（螺旋桨） starts to work. They push the robot a short distance away from the building, while the ropes slide along a railing（栏杆）to carry the robot over to the next window. Then, as a different set of propellers holds the robot tight against the window, the cleaning cycle repeats. Oliver tested his robot by cleaning sample windows he'd built in his backyard. The robot’s propellers can hold the robot against a building even in winds as high as 45 kilometers per hour, the teen reports. He performed those tests using his family’s leaf blower.

Besides limiting the chance of injury, this window-washing robot could save building owners a bit of money. If commercialized, Oliver estimates it would cost about ＄11,000. That's about the same cost as hiring a crew to clean a 7-story building. So Oliver suspects his robot might be able to pay for itself after cleaning just one such building.

1.What encouraged Oliver to develop his project?

A.His interest in housework. B.The accidents he experienced.

C.The high costs of washing windows D.Risks facing high-rise window washers.

2.What do we know about the robot?

A.It carries water itself. B.It is supported by a platform.

C.It hangs from ropes while working. D.It can produce power while working.

3.Why did Oliver test his robot with a leaf blower?

A.To record its working speed B.To see its wind-resistance ability

C.To test whether it could remove the windows D.To know if it needed a different set of propellers

4.What does the last paragraph imply about the robot?

A.It is costly but time-saving. B.It still has many limitations.

C.It has huge commercial potential D.It has become a favorite of building owners