Question

In the cardiac cycle,

A. the right atrium and the right ventricle contract simultaneously.
B. the two atria relax while the two ventricles contract.
C. the left atrium contracts before the right atrium.
D. all four chambers of the heart contract at the same time.
E. all four chambers of the heart are in systole at the same time.

Answer 1

That would be B.

During ventricular systole both atria relax while the 2 ventricles contract and send blood into the arteries.

The rest of choices are wrong,
The atria contract at the same time.
All 4 chambers never contract or are in systole at the same time.