Russia has few ocean ports that are. a)closed year-round. b)able to accept more than one type of ship. c)free from ice year-round. d) usable for ships constructed in the past 20 years ​

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.