大学英语四级语法大全目录
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。
英语四级语法：be going to / will
大学英语四级语法大全目录
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.
英语四级语法：should 和ought to
大学英语四级语法大全目录
should 和ought to 都为"应该"的意思，可用于各种人称。
---Ought he to go?
---Yes. I think he ought to.
表示要求，命令时，语气由 should(应该)、had better最好)、must(必须)渐强。
From:https://www.zgghmh.com/CET-4/20001059.asp