While there are signs that a mushroom is poisonous, they are not consistent, and all mushrooms of unknown origin should be considered dangerous to eat.

尽管有特征说明蘑菇是有毒的，但它们是不一致的，所有来历不明的蘑菇都应该被认为是有危险的食物。

youdao

Their language is of unknown origin and cannot be placed within any standard classification.

他们的语言起源不明，也无法被归入任何标准的类别。

youdao

It is very important that fevers of unknown origin in people coming from these endemic areas be investigated for the possibility of Lassa fever.

对来自地方性流行区，出现不明原因发热的人进行检查，确定是否感染拉沙热是很重要的。

youdao

If you have a temperature of 101 F (38.3 C) or higher for more than three weeks and your doctor isn't able to find the cause after extensive evaluation, the diagnosis may be fever of unknown origin.

CNN: Fever