Which one of these is NOT an example of inter-cellular communication?
A.) chemical signal from pituitary gland to adrenal gland
B.) a vesicle encloses over a nutrient molecule
C.) chemical messengers dock onto receptors of adrenal gland
D.) electrical signals pass between heart cells
Please help me I've been on this question for over an hour. I'm sure it's literally the simplest thing, but I'm not getting it. :(