weak acid

例句：

1. 1. The old man was so weak that he couldn't lift his own weight.
   老人虚弱到连自己的体重都提不起来。
2. 2. The baby is weak and needs to be fed frequently.
   婴儿虚弱，需要经常喂食。
3. 3. The team lost its last match due to a weak defense.
   由于防守不力，球队在最后一场比赛中失利。