A: are you sure that your home work do correctly?
B: i am not sure, because i not do this homework with carefully, how about you?
A: of course, i sure my home work do correctly ... because  i do that home work with carefully 
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A : What do you think about the mathematic test yesterday?
B : I'm not sure about it. I think I will get bad score
A : You must be optimist. I'm sure that you will get good score
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