In the Section "Investigating Life: the Nerve of Those Clams!",which

In the section "Investigating Life: The Nerve of Those Clams!",which of the following was the dependent variable?

A) the concentration of toxin fed to the clams
B) the rate of Na⁺ flow across the membrane of the clam neuron
C) the ability of clams to burrow
D) the location from which the clams were isolated
E) the species of algae fed to the clams