Largest change in the water level Which would produce the largest change in the $\ce{H2O}$ level when added to water in a $\pu{25 mL}$ graduated cylinder?
(A) $\pu{10.0 g}$ of $\ce{Hg}$ $(d = \pu{13.6 g/mL})$
(B) $\pu{7.42 g}$ of $\ce{Al}$ $(d = \pu{2.70 g/mL})$
(C) $\pu{5.09 g}$ of iron pyrite $(d = \pu{4.9 g/mL})$
(D) $\pu{2.68 g}$ of oak $(d = \pu{0.72 g/mL})$

I approached this question by dividing the mass by density to find the volume change. Thus, I got the answer (D), but the answer is (B).
Can anyone please explain this?
Because it’s density is less than 1, the oak floats. 

Therefore it displaced less than its full volume; some of the floating oak is above water. 

Since it’s 2.68g of oak, it displaces only the volume equivalent to 2.58g of water.