题目内容：

Airplane emissions are a big problem for the climate—and steadily rising. Experts predict that aircraft emissions will triple（增三倍）by 2050 as demand for flights increases. To prevent this terrible situation, a team of scientists at the Massachusetts Institute of Technology, along with government and industry partners, is attempting to completely redesign airplanes.

Their idea, called the “double-bubble” D8, could significantly reduce plane’s carbon footprint and improve fuel efficiency if confirmed in full-scale tests. It involves major changes to the standard 180-passenger Being 737 and Airbus A320 aircraft.

The most significant change, though, is where the engines are fixed. Air slows down as it flows over the top of a traditional plane, thus creating drag and making the craft less efficient. But the D8 design moves the jet’s engines from their usual spot underneath the wings to the top of the plane’s body, by the tail—where they suck in and speed up the slow layer of air, greatly reducing drag.

These changes would make the aircraft use 37 percent less fuel than a typical passenger jet. The experts have already built and tested an 11th-scale model of the aircraft in a NASA wind tunnel. Combining the new design with future technological advances could further reduce fuel use and finally add up to 66 percent in fuel savings in two decades.

Other experts note that the D8’s develops must still overcome economic difficulties while ensuring that the engines are strong enough to handle the new design. Still, “it’s a very remarkable idea and design,” says Brian J. German, an aerospace engineer at the Georgia Institute of Technology, who was not involved in the work. The experts are now exploring the development of a half-scale model plane. If the effort succeeds, travelers may fly in one of these jets as soon as possible.

1.Why are airplane emissions steadily rising?

A. Because of the special climate.    B. Because of designing new airplanes.

C. Because of the increasing flights.    D. Because of the development of industry.

2.What are the most obvious changes of the new airplanes?

A. Their engine shape.    B. Their engine weight.

C. Their engine position.    D. Their engine power.

3.How do the experts reduce pollution from planes?

A. Using 11th-scale models.    B. Saving energy.

C. Inventing stronger engines.    D. Improving typical passenger jets.

4.How is the new plane progressing?

A. It meets with economic difficulty.    B. It is at the laboratory stage.

C. It may fly as soon as possible.    D. It is testing with its new engine.