The majority of aberrations are sporadic although on rare occasions a chromosomal disorder is directly inherited.

尽管偶尔可见一种染色体疾病是直接遗传的,但是大量的染色体异常是散发的.

辞典例句

On rare occasions, however, a virus will infect the T cell and become dormant.

然而有极小一部分病毒感染T细胞后就处于休眠状态了.

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