425. It is unheard of to invent a new drug or cure without first having repeated failure.
沒有一次又一次的失敗，就不可能發明新藥物，找到新療法。

六級詞匯講解:
it is unheard of...意思是“未曾聽說過……，……不可能”.本句中，不定式短語to invent...作句子的真正主語。without表示否定，與前面的unheard形成雙重否定，表達肯定的意思。

句型拓展:
It is not uncommon for students to have friendly relationship with their teachers.
學生與老師建立友好關系并不罕見。
In some countries no major business is carried on without eye contact, requiring face-to-face conversation.
在有些國家，一切重大事務都要面對面地進行，需要當面交談。
There is no denying the truth.
真理是不容否認的。
There is no rule that has no exception.
任何規則都有例外。