Agriculture has no impact on the levels of organic content in soil because organic matter is plowed back into the soil every year.

Is this a true or false question, because if it is, it is false. 

Answer (d) may increase or decrease porosity through dissolution or deposition;

It is useful for historians to write narratives so that history can be passed on from their point of view.  think about a story being told in third person, then think about it again being told in first person, by someone who actually experienced the event.