1a. Make the statemens more polite.
Example: Tou're not right. (think) - I don't think (that) you're right.
1. It wasn't an explosion. (think)
2. They weren't humans. (believe)
3. James hasn't got an alibi. (think)
4. Scientists can't explain their disappearance. (believe)

1. I don't think it was an explosion. 2. I believe they weren't humans. 3. I think that James hasn't got an alibi. 4. I believe that scientists can explain their disappearance.