The posterior vena cava:

The sinu-auricular valve occurs in which of the following locations?

Select the correct option:
$(1)$ The pericardium is a double-layered membrane surrounding the heart.
$(2)$ The $SA$ node has a higher rate of impulse generation compared to the $AV$ node.

The nature of the valves in the heart is:

Blood pressure in the pulmonary artery is

Which organ is important as a large reservoir of erythrocytes?