Sedimentary rocks are made of once-living things or their pieces. a. organic b. inorganic c. chemical d. fragmental

I believe the answer is A. Hope this helps.

A. Organic

Explanation:

Once living things have rocks that are made up of organic content as sedimentary rocks are best suited to preserve the remains of the fossils and for keeping records.  The organic sediments in rocks are formed due to the accumulation of organic debris collected from various natural sources. As there are swampy sediments that contain various carbon traces and are black, and soft.  Fossils are very important elements of depositional environment and especially trace fossils like burrows, footprints and leaf impressions, etc. Some examples of corals and other shell fossils indicate marine deposition.