Please learn to spell "grammar" correctly -- and please do not use all-caps in your writing. It's considered rude (shouting) when you're writing online.
1. by (not under) -- I don't understand the meaning of the second half of the sentence.
2. He has not been heard of for years. No one knows what has become of him.
3. "Do you believe in ghosts?" I asked. (The rest is correct.)
4. can't (not "cant")