She wasn't born yesterday.
她又不是三岁小孩

You can't fool her.She wasn't born yesterday.
你骗不了她，她又不是三岁孩子。
Don't try to cheat me, I wasn't born yesterday.
不要试图欺骗我，我又不是三岁小孩。

A:Susan,do you want to drop by Tom's with me tonight?I hear he's having a party.
苏珊，今晚你愿意和我一起去汤姆家吗？我听说他在举办晚会。
B:I wish I could.But I promised to run errands for my mom.I don't think I can get out of it.
我希望我能去。但是我已经答应了我妈妈帮她做点事。我觉得我可能推不了。
A:You could tell her something important came up.
你可以告诉她你有点着急的事情要做。
B:Like what?
比如呢？
A:You could say that an old friend turned up and that you wanted to see her.
你可以说，来了一个好朋友，你想见她。
B:I don't think she'll believe such excuses.She wasn't born yesterday,you know.Maybe I can come later on.
我觉得她不会相信这种借口。她又不是小孩子。没准我可以晚点去。