able
1.able后面的不定式通常不属于被动语态，如通常不说The mistake is able to be corrected，最好改作The mistake is capable of being corrected。
2.able指能力，不一定意味着实行，如“经过了两个月的步行，他们到达了目的地”通常不说After a two-month tramp they were able to reach their destination，而用下面的任何一种：
- After a two-month tramp they reached their destination.
- After a two-month tramp they succeeded in reaching their destination.
- After a two-month tramp they managed to reach their destination.
