用所给单词的适当形式填空.

用所给单词的适当形式填空.
Many people today like reading stories about UFOs.Many people in different countries are 1.___ the UFOs.But what are UFOs?
There are some different saying for UFOs.2.___ those saying,the most popular one for UFOs is that they carry visitors coming from other stars.They 3.___ to fly much faster than planes to the earth.
UFO scientists and many people 4.___ this saying.Some people said that they saw a few UFOs that 5.___ landed on earth.Some people said they saw some strange visitors coming out of the UFOs.Some even said they were carried away in the UFOs,and then were sent 6.___ by the strange visitors.
Some people make mistakes when they say they have seen UFOs.7.___ they see a weather 8.___ or an uncommon plane,or the light they see in the sky comes from the ground.Sometimes they see the light from moon.
But there are a lot of things we can't 9.___ .Now,people still can't understand UFOs clearly.It may take many years to find a clear 10.___ and then people will give UFOs another name.
选填的词有：among,of,believe,seem,reply,back,balloon,study,perhaps,understand,answer,land