真的?
Really? “真的吗?”询问对方的语气，也常说Oh, really?
-He's 38. (他38岁。)
-Really? (真的?)
Are you sure? *“敢肯定吗?”，想要确认的心情，要比上句稍强。
你是认真的吗?
Are you serious?
-I want to break up with you. (我想和你分手。)
-Are you serious? (你是认真的吗?)*有些怀疑对方的语感。
开玩笑呢吧?
Are you joking?
-I quit my job. (我把工作辞了。)
-Are you joking? (开玩笑呢吧?)
Do you mean it? (是真的吗?)
Are you kidding? (是说着玩吧?) *kid 常来表示“耍弄，开玩笑”。
我怀疑。
I doubt it. *表示对别人的话抱有怀疑的心情。
-Do you think you'll get a raise? (你觉得你能涨工资吗?)
-I doubt it. (我怀疑。)
It's doubtful!
I don't think so. (我不这样认为。)
I wouldn't bet on it.
It's chancy. *俚语。
It's iffy. *非常随便的说法。
听起来可疑。
It sounds fishy to me. *fishy 除了表示“鱼的，像鱼的”之外，它还有“靠不住的，可疑的”意思。
-What do you think? (你怎么想?)
-It sounds fishy to me. (听起来很可疑。)
It sounds suspicious to me.
It sounds funny to me.
Something's fishy.
I smell a rat. *smell a rat 为短语，表示“感到有可疑之处”、“事情很可疑”的意思。
我不信他的话。
I won't buy that story. *此处的buy表示“相信(believe)，当真”，而不表示“买”，口语中常用。
-He said she is his sister. (他说她是他的妹妹。)
-I won't buy that story. (我不信他的话。)
-But, it's true. (可那是真的呀。)
-I don't buy it.
你认为她是当真的吗?
Do you think she's serious?
-She told me she likes you. (她告诉我她喜欢你。)
-Do you think she's serious? (你想她是认真的吗?)
我不把他的话太当真。
I don't take him too seriously.
I don't pay much attention to what he says. *pay attention to...“对……严加注意”、“对……留意”。
我不相信他。
I don't believe him. (我不相信他。)
-What makes you say that? (你为什么这么说呢?)
-I don't trust him.
I don't think he is telling the truth. (我认为他没说真话。)
I think he is lying. (我认为他在说谎。)
有这么好的事!
It's too good to be true. *直译是“说得太好了”，表示事情或情况好得过分。
-I won two tickets to Hawaii! (我赢了两张去夏威夷的票。)
-It's too good to be true. (有这么好的事!)
It's so unbelievably good that there has to be something wrong. (哪有这么便宜的事!)
Nothing this good ever happens, it must be a mistake. (不会有这么好的事，一定是搞错了。)
It can't be! It's too good to believe! (怎么可能!好得让人难以置信。)
上述就是关于“怀疑”态度的一些托福口语表达方式，大家可以看到，不同的情景会有不同的表达， 这个还需要大家在托福口语备考中多积累、多扩展。