Answer:
D.
Explanation:
it’s D. Because the tone is pretty much the attitude.
The correct answer is <em>who.
</em>The teacher knew it was Sam who was passing notes.
It would be <em>whom </em>in this case:
The teacher knew it was Sam <em>whom </em>they were passing notes to.
I think 1.He left school three years ago is the right answer.