One Hypothesis Explaining Animals' Abilities to Detect a Magnetic Field

One hypothesis explaining animals' abilities to detect a magnetic field and use it to navigate is that sensory cells detect electrical fluctuations influenced by Earth's magnetic field. Which of the following pieces of evidence, if it were true, would support this hypothesis?

A) Sensory cells of an organism known to use magnetic fields to navigate show an increase in action potential firing when in the presence of electrical fluctuations.
B) Sensory cells of an organism known to use magnetic fields to navigate show a decrease in action potential firing when in the presence of electrical fluctuations.
C) Sensory cells of an organism known to use magnetic fields to navigate show a greater density of negative ions on the outside of its plasma membrane.
D) Sensory cells of an organism known to use magnetic fields to navigate produce greater amounts of enzymes sensitive to electrical fluctuations.