第一句：That's my conviction.
A: Do you think my ankle will be better by Sunday, doctor?
B: I suppose so.
A: Are you quite sure?
B: That's my conviction.
第二句：I have no doubt about it.
A: Do you think Mr. Green will quit his present job?
B: Yes, I have no doubt about it. He complained abou the low pay more than once.
I can easily believe is. 我容易相信这种说法。
I think it's believable. 我认为那是可信的。
I'm a hundred percent certain. 我百分之百相信。
I'll take your word for it. 我相信你的话。