George B
Extinct but not forgotten Staff Member
"are thought possible" is true. So you can't use that.
You need a statement that, if true, would actually mean something. Of course some people think some things are possible.
How about . . .
"Someone is deliberately spraying substances (other than normal emissions) from jet aircraft, at altitudes above 30,000 feet, and below 100,000 feet, for secret purposes,and these substances because they are in addition to normal emissions form long white visible trails that last for extended periods of time even when normal contrails would not persist . . . ."