extremely rare

基本解释

It is an extremely rare and lethal haemorrhagic fever, closely related to Ebola, for which there is no known cure.
这种病毒是一种极为稀有与致命的出血热，并且与无法治愈的埃博拉病毒关系密切。
The group is receiving new cases at a rate of about one a week, many of which are extremely rare at such young ages.
该组织目前正以大约每周一例的速度接收新的病例，其中许多疾病发生在如此年轻的人身上是极为罕见的。
But other scientists have warned that the cure only worked because the donor was both compatible and carrying an extremely rare double HIV resistant mutation in his genes.
但是其他科学家警告称，这次治疗之所以成功，是因为（骨髓）捐献者配型成功，并且基因中含有极其罕见的抗HIV突变。

He says young dinosaur fossils are extremely rare, a possible sign that many of them had been eaten by attackers.
Reports of solar system objects striking each other are extremely rare.
"And to break records by that sort of margin is something which is extremely rare."

But I was told that sequential paralysis of one vocal cord following another is extremely rare.
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