1）當let後只有一個單音節動詞，變被動語態時，可用不帶to 的不定式。
they let the strange go.---> the strange was let go.
2） 若let 後賓補較長時，let 通常不用被動語態，而用allow或permit 代替。
the nurse let me go to see my classmate in the hospital.
----> i was allowed / permitted to see my classmate in the hospital.