I would go for D but if in doubt go for B
Answer:
An impulse travels from one nerve to another by release & subsequent diffusion of chemicals called neurotransmitters across a very small gap between neurons, called a synapse.
Explanation:
So in this case it would be transmitted via the cell membrane (Synapse)
Liquid: D
Gas: B
Solid: C
Plasma: A
Hopefully these are correct.
Have a great day :)