1)当let后只有一个单音节动词,变被动语态时,可用不带to 的不定式。 They let the strange go.- The strange was let go.
2) 若let 后宾补较长时,let 通常不用被动语态,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.