The correct answer is - A. coal.
The coal is classified as organic sedimentary rock because the basis for its formation is the organic matter. It is a rock that is formed on the basis of dead organic matter from the Carboniferous, mostly of trees that existed in this period. Over a long period of time, tens and hundreds millions of years, the coal, under all the temperature and pressure that had influenced it started to take the shape in which we now know it. It can be mixed with other material, but in general comes in the non-mixed organic based form.