On a topographica map contour lines that form a circle indicate a. a lake b. a hill c. an ocean d. a depression

Usually a hill (B).  But a circular ditch, depression, or tapered hole in the ground would also show circular contours.

a mid-ocean ridge or mid-oceanic ridge is an underwater mountain range, formed by plate tectonics. this uplifting of the ocean floor occurs when convection currents rise in the mantle beneath the oceanic crust and create magma where two tectonic plates meet at a divergent boundary.a geomagnetic reversal is a change in a planet's magnetic field such that the positions of magnetic north and magnetic south are interchanged.