Arteries are distinguished from veins based on all of the following features except a the direction of blood flow relative to the heart. b the amount of oxygen present in the blood. c the structure of their walls. d the blood pressure. e All of the choices are correct.

Which statement about relative potential energy of electrons is correct? a. an electron in the 2 p orbital of the second electron shell has more potential energy than an electron in the 2 s orbital of the second electron shell. b. an electron in the 2 p orbital of the second electron shell has more potential energy than an electron in the 3 p orbital of the third electron shell. c. an electron in the 3 p orbital of the third electron shell has more potential energy than an electron in the 2 p orbital of the second electron shell.