I（主语） can't decide（谓语） which pair of jeans to buy（动词不定式短语作宾语）这个句子,译为汉语的意思是“我拿不准该迈哪条牛仔裤”.
which pair of jeans to buy是动词不定式短语,它的表达和我们汉语正好相反,因为按照英语直译就是“哪条牛仔裤要买”,而汉语则说“要买哪条牛仔裤”.
They both look good on me .可以译为：（这两条牛仔裤）我穿着都好看.（直译：它们在我身上看起来都好.）
I can't decide which pair of jeans to buy .They both look good on me .我拿不准该迈哪条牛仔裤,（这两条牛仔裤）我穿着都好看.
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