1. fall─fell─fallen落下；跌倒
      fall asleep睡着/fall behind落后
      例句：①An apple fell to the ground.(一个苹果落在地上。)
      ②Be careful on the ice or you will fall.(在冰上要小心，否则你会跌倒。)

2. feel─felt─felt
      feel like＋doing sth.想要；
      feel sleepy.想睡
      例句：①Can you feel your heart beat violently?(你能感觉到你的心在猛烈地跳动吗？)
      ②Both my legs didn’t feel.(我的双腿没有感觉。)
      ③I suddenly felt a pain in my back.(我突然感到背部疼痛。)
      ④Do you feel like taking a walk?(你想不想去散步？)

3. fell─felled─felled砍伐
      例句：A lot of trees were felled last night.(昨晚很多树被人伐倒了。)

4. fail─failed─failed失败
      例句：He has failed in English exam again.(他英语考试又没及格。)