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。

be going to / will

用于条件句时， be going to　表将来

　　　　　　　 will　表意愿

　　If you are going to make a journey, you'd better get ready for it as soon as possible.

　　Now if you will take off your clothes, we will fit the new clothes on you in front of the mirror.

be to和be going to 

　　 be to 表示客观安排或受人指示而做某事。

　　 be going to 表示主观的打算或计划。

　I am to play football tomorrow afternoon.　　 (客观安排)

　I'm going to play football tomorrow afternoon. (主观安排)