Which best describes the pericardium? structures inside the heart that ensure that blood flows in one direction only
a sac around the heart that allows the heart muscle to receive oxygen
a sac around the heart that protects the heart and chest tissues
structures inside the heart that bring blood to the lungs for oxygenation

Which of the following types of stars is most likely to end up as a supernova? in graph a, the curve peaks at 800 nm, in the red section of the visible light spectrum. in graph b, the curve peaks at 550 nm, in the green section of the visible light spectrum. in graph c, the curve peaks at 450 nm, in the blue section of the visible light spectrum. in graph d, the curve peaks at 300 nm, in the violet section of the visible light spectrum. a b c d