Analogy - porosity is to holes as permeability is to _
a. cracks
b. soild rock
c. filled-in pores
d. closed pores

Porosity is the amount of empty space in a rock or other earth material (like sand) - in other words, it's how much water a material can hold. 

Permeability refers to how well water flows through a material - the flow is controlled by how large the pores are and how well connected the pores are in a given object.Therefore, there these are two primary factors that limit the movement and the amount of water (or other fluids) retained  in rocks/sedimentary materials.