11.3 used to / be used to
 
  used to + do:"过去常常"表示过去习惯性的动作或状态,但如今已不存在。
  Mother used not to be so forgetful.  
  Scarf used to take a walk.  (过去常常散步)

  be used to + doing: 对……已感到习惯,或"习惯于",to是介词,后需加名词或动名词。
  He is used to a vegetarian diet.  
  Scarf is used to taking a walk.(现在习惯于散步)

典型例题   
---- Your phone number again? I ___ quite catch it.
---- It's 69568442.      
A. didn't  B. couldn't C. don't D. can't
  答案A. 本句虽没有明确的时间状语,但从语意上看 出,在听的时候没有听懂这个动作发生在过去,因此应用过去时。