The principal question in drug design is how to study the ligand-binding sites and others because of the poor structure information.

如何在生物胺受体结构数据严重匮乏的基础上研究受体的配基结合位点及其它功能位点，已成为药物设计中的关键问题。

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National Public Radio asked exactly this question in a survey a year or so ago and they got the following principal responses back.

国家公共广播电台问过,完全相同的问题,在一次一年前的民意调查中,他们得到了如下的回复

耶鲁公开课 - 聆听音乐课程节选

That's a good question. As a parent or as a principal?

这个问题很好。从父母还是校长的角度来说呢？

驯服淘气的人 - SpeakingMax英语口语达人

Incredibly, there was but one panel held in the plenary hall that had as its principal subject the question of national defense.

CENTERFORSECURITYPOLICY: "Where's the rest of me?"

The principal reason for the delay was the ever divisive question of who would control the country's immense oil wealth.

FORBES: Slick Solution

But others question the likelihood of success without reducing the principal.

ECONOMIST: The foreclosure plan