Axis of vertical aerial photograph coincides with the _______

The characteristics of contours are given in statements S1, S2 and S3.

S1: Two contour lines of different elevations can cross each other in the case of an overhanging cliff.

S2: Generally the contour lines do not cross a valley or a ridge line at the right angle.

S3: A contour line passing through a point is at the right angle to the line of maximum slope at that point.

Identify the wrong statement(s).