How are mid-ocean ridges and trenches similar, and how do they differ?

this is a science question i just cannot figure out. please help. thank youHow are mid-ocean ridges and trenches similar, and how do they differ?
Mid ocean ridges occur at constructive plate boundaries where 2 oceanic plates are moving apart. The ridge is made up of the extruded lava that wells up when the plates move apart. The best example of one is the Mid Atlantic Ridge.





Ocean trenches occur in front of subduction zones, also known as destructive boundaries. This is where one plate is sinking beneath another. Where the plate being subducted goes down it forms a very deep trench. Examples would be off the coast of Chile or the Marianas trench on the other side of the Pacific.





This is just very basic but hopefully gives you enough of an idea to find out whatever else you need.How are mid-ocean ridges and trenches similar, and how do they differ?
here are some pics, they should help





http://www.ess.washington.edu/SEIS/PNSN/鈥?/a>





http://sio.ucsd.edu/volcano/about/subduc鈥?/a>





Similar: because they part of plate tectonics





Differ: mid ocean ridges- like a mountain that is continually separating


Trenches- a deep trench, where one plate subducts under another plate