Which would produce the greatest change in the water level in a 25mL graduated cylinder?

a)7.42g of Al (d=2.70 g/mL)
b)2.68g of oak (d=0.72g/mL)

The answer is a) but I can't see why...

It is not the total volume that counts for raising the water level, it is the volume below the water line. The oak floats. The volume of the oak is 3.72 ml, but only 2.68 ml is below the water line. All of the Al (2.74 ml) is below the water line.