未灰心的

例句：

1. 1. The team is undefeated in their last five matches.
   该队在最近五场比赛中保持不败。
2. 2.The champions are undefeated until now.
   直到现在，冠军队一直保持不败。
3. 3.The player was undefeated in the tournament.
   这位选手在锦标赛中保持不败。