I think i see what he means the answer is B.
but correct me if i'm wrong.
The answer is hard tissue.
Usually, hard tissue, such as bones and teeth or exoskeleton is much more preserved than soft tissue (organs, skin, etc.). Fossils become fossils by a process of mineralization. Hard tissues are more mineralized during life than organs. So it is no surprise that hard tissues take part in the process of mineralization and is preserved in fossils, unlike soft tissues.
Answer:
Well, Earth is the same way! Earth is made up of several different layers, each of which has unique properties. Both parts of the core are made up of mostly iron and some nickel. The difference is that in the inner core, those minerals are solid and in the outer core, they're liquid.
