Question

1/People say that he saw a UFO last night. => => 2/They don't think that ghost exists. => => 3/We think that you were at the party last night. => => 4/People say that that man is a cold-hearted one. => =>

Answer 1

1 it is said that he saw a UFO last night

He is said to have seen a UFO last night

2 It isn't thought that ghost exists

Ghost isn't thought to exist

3 It is thought that you were at the party last night 

You are thought to have been at the party last night

4 It is said that that man is a cold-hearted one

That man is said to be a cold-hearted one