Finally, some evidence also suggests that an unknown factor in human milk may cause breast-fed infants to produce more fibronectin on their own than do bottle-fed babies.

最后，一些证据也表明，相对于奶粉喂养的婴儿，一种母乳中的未知因子可能会使母乳喂养的婴儿产生更多的纤维连接蛋白。

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Multiple-expansion is always an unknown factor in predicting stock returns.

FORBES: The Next 10 Years