有些拷贝数变异是很常见的，但还有一些则在人类中极少发生或是发生的频率较低。
Some CNVs are common, but others are rare or occur with low frequency among humans.
另一个例子是数星期前发生的。
出血可能发生在术后数小时或甚至几天。
Bleeding may occur for several hours, or even a few days after surgery.
分析表明，该真随机数发生器具有良好的性能。
Analysis shows that this true random number generator has good performance.
他数星期来，有好几次在眩晕前，意识突然发生变化。
He had several sudden alterations in consciousness preceded by dizziness for several weeks.
但是实际上留数却确实会发生变化。
但是实际上留数却确实会发生变化。
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