This centers is correct ?? They must have cheated the today's test so I should have advice to teacher. 彼らは今日のテストでカンニングしたに違いない、だから先生に教えるべきだった。 He may have already knew this things therefore I needn't have send e-mail to Mr. Kim. But some people can't have told this things to Mr. Kim. 彼はこの事をすでに知っていたのかもしれない、だから　私はキムにメールを送る必要はなかった。でも、誰もキムにその事を教えたはずはないのに。 助動詞の勉強中です。 Should have must have can't have may have needn't have