看Flash学口语:表示怀疑_初级英语口语

对此半信半疑.
I'll take that with a grain of salt.
take sth with a grain of salt:to be careful about believing that sth is completely true 不完全相信:半信半疑

我对此表示怀疑.
I doubt it.
I am still skeptical.
我仍表示怀疑.
Skeptical: 怀疑的,多疑的 ( about/of)
Many were skeptical about this solution.
许多人对这一解决办法表示怀疑.
I am sceptical about his chances of winning.
我怀疑他取胜的可能性.
The public remain sceptical of these claims.
公众对这些说法仍持怀疑态度.
She looked highly sceptical.
她一脸深表怀疑的神色.

你蒙不了我.
You can't fool me.
Fool: to trick sb into believing sth that is not true 欺骗;愚弄
She certainly had me fooled─I really believed her! 她确实把我骗了 我真的相信了她的话!
You don't fool me! 不要骗我!
You're fooling yourself if you think none of this will affect you. 你要是认为此事一点也不会影响你,那就是欺骗自己.
Don't be fooled into thinking they're going to change anything. 别上当受骗,以为他们打算作出任何改变.

我要亲眼见到才能相信.
I'll believe it when I see it.
Seeing is believing.
眼见为实.

我又不是三岁小孩.
I wasn't born yesterday.
句型"I was born..."表示"我出生于...".

他的决定值得怀疑。
His decision is doubtful.

别指望我会相信你。
Don't expect me to believe you.
I don't believe you. 我不相信你.

我不相信广告。
I don't have belief in ads.
ad = advertisement"广告"

别瞎说了!
Get out of it!
Never tell me!
我才不信呢!

你得了奖学金？! 我才不相信你的鬼话呢。
You have won the scholarship?! I don't buy it.
Buy: to believe that sth is true, especially sth that is not very likely 相信(尤指不大可能的事)
You could say you were ill but I don't think they'd buy it (= accept the explanation).
你可以称病,但我想他们不会相信的.