例如：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.