What is an important part of the endocrine system that acts as a chemical messenger? hormones

arteries

spinal cord

neurons

Iknow the answer to 13 is b and 14 is d. i just need to know why the correct answers are correct

Which theory was contradicted by experiments with the photoelectric effect? light spreads out after it passes through a small opening. as soon as light strikes metal, electrons will be ejected. visible light, regardless of color, will cause the ejection of electrons when striking metal. the kinetic energy of ejected electrons depends on the frequency of light that strikes the metal.

Element before carbon on the periodic table