“做决定”的地道表达

1I've decided. 我已经决定了。
2I've made up my mind. 我已经做好决定了。
3I've come to a decision./I've made a decision. 我已经决定了。
4It's hard to decide.这很难决定。
5I'm sure I can do it. =I certainly can do it.=I believe I can do it.我确信我能做好。

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