Im not sure if this is right or not but i think it might be C.
Hope its right!!!!
Sample A most likely came from the left ventricle, as this is the portion of the heart that receives freshly oxygenated blood to be pumped to different parts of the body. Oxygenated blood is blood that has had oxygen bounded to it by hemoglobin (a pigment made of iron found in red blood cells). The oxidation of this blood by the iron in the hemoglobin gives it the RBC bright red look. This blood containing the bright RBCs in transported to the left ventricle from the lung, after which it is spread throughout the body. Hence, in normal conditions of the heart, the Sample A most likely came from the left ventricle.
Well, an endoskeleton is an internal skeleton, like humans have.
Pro: Bones do not get broke as easily, since they are inside of the body. Bones that break also heal more quickly in an endoskeleton, since they have tissue and blood surrounding it and transferring nutrients.
Con: The flesh can get easily damaged. There is no shedding with endoskeletons, so a new skeleton cannot be grown in the event of an injury.