When, if ever, is it morally justifiable to allow a patient to die?

假如可以的话，什么情况下允许病人放弃生命在道德上是正当的？

《柯林斯英汉双解大词典》

A patient may also acquire a tolerance for a certain drug, which means the patient has to take ever larger doses to produce the desired effect.

患者还可能对某种药物产生耐受性，这意味着患者必须服用比以往更大的剂量才能产生预期的效果。

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The noisiest patient I ever had was a young man suffering from a disorder affecting one of his ureters.

我最不安静的病人是一个患有一侧输尿管功能紊乱症的年轻男人。

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In 1990, he pioneered the first-ever patient navigation program, training people from the community to listen and answer questions after a diagnosis.

CNN: Helping patients navigate the health care system

The first ever national patient survey confirms that patients trust and value their GP.

BBC: News | UK Politics | Frank Dobson's speech in full

But Mr Obama is distrusted in Israel, has no viable plan, and has just lost the ever-patient George Mitchell as his envoy.

BBC: Arab Spring headaches for Barack Obama