所有参赛选手中，他的观察力最为敏锐。

Among all the contestants, his observation was the ___keenest.

他是班上对科学实验最热心的学生。

He is the ___keenest student in the class when it comes to science experiments.

她最敏锐的评论总是能直击问题的核心。

Her ___keenest remarks always hit the heart of the issue.