After the fossils are buried in the mud the soft tissues start to decompose rapidly. Leaving only the hard shells or bones of the animal. With time, sediment starts to build up on the top and then hardens into rock. The bones then start to decay, minerals start to enter and then end up replacing the organic material cell by cell in a process that is known as "petrification." So the answer you are looking for is B, Mud can prevent oxygen from reaching the dead organism.
Maybe say something along the lines of " parasites are complex and very harmful" and build off of that statement
The Answer Is Deep Sea TRENCHES
