1. Most of what he say is true.

2. Most of the people were engineers.
3. Most of the water was bad.
4. Mos of his books were old.
5. Most of books were old.
6. Most books were old.
7. Half of his time was wasted.
8. Half of the apples were bad.
9. Half of the apple was bad.

(Which ones are ungrammatical?)

1. Most of what he says is true.

2. Correct
3. Correct
4. Most of his books were old.
5. Most of the books were old.
6. Correct -- but a little confusing.
7. Correct
8. Correct
9. Correct