Can someone plz help me if u can’t see zoom in plz help me

City 1 and City 2

Step-by-step explanation:

The water is moving down stream, moving from City 1-2-3-4 in that order.

if water was taken a the X mark, the pollutants would have to have come from the cities above where the sample was taken.

Hope this helps!

City 1 and 2.

Step-by-step explanation:

To be completely honest I have never done a problem like this before but I am fairly confident with my answer. As it can't be city 3 or 4 as they are after the polluted water sample was taken and the river is flowing down. The only two options it could be is city 1 and 2.

I hope this helps!