What does a UFO look like? Do you believe there are aliens outside the earth? Maybe nobody can tell us exactly, but some of us believe that we humans are not alone in this world. We have friends living outside the earth. And a lot of people in the world think they really have seen a UFO flying in the sky. Now many scientists are trying to understand the origin of the UFO sightings. Scientists even try to draw pictures about aliens and aliens’ life according to their imagination.        
Because we don’t really know about it, we call it UFO or Unidentified Flying Object. Many of us are curious(好奇的) about it and interested in it very much.
While scientists have no same ideas about whether there is an alien or not, it seems that China has been home to some UFO sightings recently.
On August 20^th,2011, a UFO was seen at 21:00 by the pilot on the plane which took off from Pudong International Airport to Changchun. At almost the same time, many astrophiles(天文爱好者)took pictures of it. Later, reports from some cities said that the UFO was seen. The pilot said the UFO was small at first, then expanded(扩大),moved north, and disappeared(消失)several minutes later. However, he couldn’t exactly make sure about what he had seen.
What do scientists know about the aliens according to this passage?

A．Scientists know about the aliens’ life well.

B．Some scientists try to imagine aliens’ life.

C．Scientists have the same idea about the UFO.

D．Many scientists have already understood the origin of the UFO sightings.

What happened on August 20^th,2011?

A．A UFO took off from Pudong International Airport.

B．A pilot took pictures of the UFO.

C．Many astrophiles saw the UFO.

D．The UFO was small when it moved north.

Which of the following sentences is NOT true according to this passage?

A．UFO is short for Unidentified Flying Object.

B．Some people from some cities said that they saw the UFO on August 20^th,2011.

C．The pilot could exactly make sure what he had seen.

D．Many of us are interested in the UFO.