12.1 let 的用法
 
 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.