Assertion (A) : The walls of atria are thicker than those of the ventricles. Reason (R) : Ventricles have to pump blood into various organs at high pressure. (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A) (b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A) (c) Assertion (A) is true, but Reason (R) is false. (d) Assertion (A) is false, but Reason (R) is true.