A. Modal Verbs: The modal verbs are can, could, may, might, shall, should, will and would. The modals are used to show that we believe something is certain, probable or possible, talking about ability, asking permission making requests, and so on.
B. Can, could and (be) able to
C. Can, could and could have, could (do) and could have (done)
D. Must, have to, can’t, mustn’t and needn’t: have to and much; Must and can’t; Must, mustn’t and needn’t