Did you know that most times if you put them all into one box then hit done it will keep the ones you got right and pull out the wrong ones. There are only two possible choices for each on. anyway.
1,2,5,6 goes with outdoor pollution.
and 3,4 go with indoor pollution.
I hope I helped.
I would help but I see no choice to choose from.
If you round it up you will get 20.
