I.1. was writing
2. was reading
3. was hearing
II. 1. He hasn't done his homework yet.
2. Have you ever been to London?
3. He has never read this book.
III. go - went - gone
drink - drank - drunk
fly - flew - flown
give - gave - given
hear - heard - heard
run - ran - run
stand - stood - stood
IV. 1. -
2. -
3. The, -
4. The, -
5. -