Many people have long dreamed of being able to fly around as simply as riding a bicycle． Yet the safety and strength of a flying bike was always a big problem． Over the past 10years， developments in technology have moved the dream of personal flying vehicles closer to reality． Now， two groups of inventors say such vehicles may be available soon．
The British company Malloy Aeronautics has developed a prototype （原型） of its flying bicycle． Grant Stapleton， marketing sales director of Malloy Aeronautics， says the Hoverbike is able to get in and out of small spaces very quickly． It can be moved across continents very quickly because it can be folded and packed， he adds．
Mr． Stapleton says safety was the company's main concern． He says the designers solved the safety issue by using overlapping rotors （ 交叠式旋翼 ）to power the vehicle．
The company is testing a full-size prototype of the Hoverbike， which will most likely be used first by the police and emergency rescue teams．
In New Zealand， the Martin Aircraft Company is also testing a full-size prototype of its personal flying device， called the Jetpack． It can fly for more than 30 minutes， up to 1，000 meters high and reach a speed of 74kilometers per hour．
Peter Coker is the CEO of Martin Aircraft Company． He said the Jetpack "is built around safety from the start． In his words， reliability is the most important element of it． We have safety built into the actual structure itself， very similar to a Formula One racing car．"
The Jetpack uses a gasoline-powered engine that produces two powerful jet streams． Mr． Coker says it also has a parachute （降落伞） that can be used should there be an emergency． " It starts to work at very low altitude and actually saves both the aircraft and the pilot，" he adds． Mr． Coker says the Jetpack will be ready for sale soon．



We can learn from the passage that the Hoverbike ______ ．

A. can hardly get in and out of small spaces quickly
B. can fly for over 30 minutes， up to 1，000 meters high
C. has been used by the police and emergency rescue teams
D. can be transported quickly after being folded and packed

The writer uses the example of For One racing car to show that ______ ．

A. the Jetpack is very safe and reliable
B. the engine of the Jetpack is powerful
C. the actual structure of the Jetpack is unique
D. the Jetpack can reach a great speed and height

The underlined word "it" in the last paragraph refers to ______ ．

A. the jet stream
B. the engine
C. the Jetpack
D. the parachute

What is the authors main purpose of writing the passage？ ______

A. To describe the problems of inventing flying vehicles．
B. To introduce the latest development of flying vehicles．
C. To show the differences between two flying vehicles．
D. To advertise the two personal flying vehicles．