Which best describes the pericardium?

a. structures inside the heart that ensure that blood flows in one direction only
b. a sac around the heart that allows the heart muscle to receive oxygen
c. a sac around the heart that protects the heart and chest tissues
d. structures inside the heart that bring blood to the lungs for oxygenation

C. a sac around the heart that protects the heart and chest tissues

Explanation:

rising temperatures because when water vapor in the air is cooled, it condenses. it turns back into a liquid and attaches to dust particles in the air. these very small water droplets group together to form clouds

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.