Which one of the following can the transit method tell us about a planet?
-its mass
-its size
-the eccentricity of its orbit

The transit method allows detecting distant planets by measuring the attenuation of the brightness of a star when a planet passes between it and the Earth.

This is done based on a phenomenon in which a body (a planet in this case) passes in front of a larger one (the star), blocking (eclipsing) its vision to some extent.  

So, this transit reflects the ratio of the size of the star and size of the planet. Hence, the larger the planet, more noticeable the eclipsing effect.

This is how the size of the star can be determined through its spectrum photometrically, although it does not give information about its mass.

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.