A student places four identical cells into four different liquids. Which cells would take in water and swell?

cells X and Z
cells W and Y
cells X and Y
cells W and Z

The gun from the crime scene shows tool marks where the serial numbers are ground off. there are also tool marks on the bullets left behind. what information can the tool marks on the bullets and gun provide about the crime? what type of evidence does this information provide, individual or class?