在一次舞会上,杰克先生看到尤妮斯一个人站在酒柜的旁边。已知:①参加舞会的总共有19个人。②有7个人是单独一人来的,其余的都是一男一女成双成对地来的。③那些成双成对来的,要么双方已相互订婚,要么双方已相互结婚。④凡单独前来的女士都尚未订婚。⑤凡单独前来的男士都不处于订婚阶段。 At a ball, Mr. Jack saw Eunice standing by the wine cooler alone. Known: ① A total of 19 people attended the ball. ② There are seven individuals are alone, the rest are a man and a woman come in pairs. ③ Those in pairs, either the two have been engaged with each other, or both have been married to each other. ④ All women who come alone are not yet engaged. ⑤ Men who come alone are not in the engagement stage.