23. 在主動脈瓣打開之後，左心室收縮情形為: (After aortic valves open, left ventricular contraction is considered:) (A)等容收縮(isovolumetric) (B)等張收縮(isotonic) (C)增滲壓力性收縮(auxotonic) (D)等長收縮(isometric)