Both coal and diamonds are forms of elemental carbon. coal is brittle while diamonds are considered to be the hardest of all substances known. what is the appropriate justification for this?

b. the carbon cycle ensures living things have a source of hydrogen

what statement best describes the difference between the sympathetic and parasympathetic nervous systems?

the sympathetic nervous system prepares the body for intense physical activity and is often referred to as the fight-or-flight response. the parasympathetic nervous system has almost the exact opposite effect and relaxes the body and inhibits or slows many high energy functions.