How can you determine which way a river is flowing on a topographic map?
Water flows Downhill. A, B, or C could be correct. You need to look at the numbers assigned to the contour lines. If there is a Valley and the contour lines show the sides of the valley then A would be correct. If there is a Waterfall then C is correct, Which would make B also correct. D is the only one not correct.
Look at the contours which cross the river. They will give to an idea of the shape of the valley and will make a "v" shape. The "V" will point uphill. If there is no obvious "V", then look at the values on the contours to see which is higher.
It is very easy on a topographic map, as those have contour lines with heights stated, and rivers of course flow downhill. On a map without topographic information and which does not include either the source of the river or the sea, it can be more difficult.