B.
1 - A
2 - B
3 - A
4 - B
5 - A
6 - A
7 - B
8 - A
C.
1. The lesson hasn’t started yet.
2. The teacher has already written on the board.
3. Joe and Tim have just come into the classroom.
4. Tony hasn’t finished getting books ready.
5. Christine has already opened the book.
6. Dave has dropped a pen on the floor.
7. He hasn’t picked it up yet.