I don't know (6)________ you've noticed (7)________ some students don't want to walk to s

I don't know (6)________ you've noticed (7)________ some students don't want to walk to school. It can be seen every day (8)________ their parents drive them to school. But nowadays, it should be brought to our notice (9)________ the air is seriously polluted. (10)________ can we do about it? Here I have a suggestion (11)________ we should ride on our bikes to school! (12)________ we can do it will not only have significant benefits for our health, (13)________ also help improve our environment. (14)________ we will have a better environment depends on (15)________ we can do for ourselves and for nature.

6. whether　  7. that　    8. that　       9. that　       10. What 

11. that　    12. That　   13. but　      14. Whether　  15. what