Santiago ramon y cajal demonstrated that a. at rest, the neuron has a negative charge inside its membrane b. neurons are separate from one another c. action potentials follow the all-or-none law d. neurons communicate at specialized junctions called synapses

b. neurons are separate from one another

Explanation:

Santiago ramon y cajal was a Spanish histologist who was born in Petilla de Aragón, and graduated from the University of Saragoza, noted for his pioneering studies in the fine structure of the nervous system. He was responsible for researching and discovering that neurons are separate from each other, furthermore, he demonstrated the basic changes of neurons during nervous system functioning. It was also the first to isolate brain nerve cells, called Cajal cells.

d is the answer

sorry if its wrong!