Just as in a supermarket , where the person at the check - out28 no longer needs to engage in29 any mental arithmetic30 , so a composition student31 may not really know how you form a dominant seventh chord32 if all he has to do is hit a command key 就像超市的收銀員不再需要任何心算一樣,學作曲的學生可以不必真正懂得如何構成屬七弦,因為他只需要點擊一下指令鍵。