I would guess that the answer would be :'<span>These organisms dig more shallow burrows than they used to.</span>' If the crabs actively dig burrows, as many crab species do, and a layer of oil has persisted in the lower soil strata, it makes sense that the crabs would be reducing the depths of their burrows to avoid contact with the oil. The other possibility is that the crabs might might migrate to deeper waters, but this is less likely because the crabs would be evolved to utilise the intertidal zone.
I believe the answer is C, Sedimentary rock.
Hope this helps.
Procedimiento para separar dos sustancias mezcladas, una líquida de otra que no lo es o dos líquidos inmiscibles (agua y aceite) mediante el vertido de la más densa.
Ehemplo: El aceite es mas dense que el agua, por lo tanto se unde hacia el fondo y el agua queda arriba.