Which of the following statements is correct about the given diagram of the cardiac cycle?

• A
  '$a$' represents atrial systole, during which $25\%$ of blood moves from atria to ventricles actively.
• B
  $(a \rightarrow b \rightarrow c)$ represents $(Atrial \ systole \rightarrow Ventricular \ systole \rightarrow Joint \ diastole)$.
• C
  '$c$' and '$d$' together are called joint diastole, during which approximately $75\%$ of blood moves from atria to ventricles passively.
• D
  '$b$' represents the phase of ventricular systole.