Sắp xếp thành câu hoàn chỉnh

collecting / Scientists / years / about UFOs / information / have spent /.
 
in our / other planets / intelligent beings/ there / on the / solar system/ Are /? /
 
has records of the United States / UFO/ including photos / government/sightings, / thousands of /.
 
UFOs are / of some people/ just the / imagination / I think/.