Answer:
B.
Explanation:
The forces that are acting up and down on the box are equal, so they cancel each other out
The forces that are acting left and right are not equal, as the force pushing right on the box overpowers the force pushing left on the box by 50 N. That means that the answer is B (as a side note, you might have accidentally switched your labels. The arrow pointing to the right means that it is pushing the box to the right).
The water can be affected by point source pollution
