他有一个敏锐的头脑来解决谜题。

He has a ___sharp mind for solving puzzles.

她是一位看似虚弱但头脑极其敏锐的老年妇女。

She is an elderly woman who seems weak but has an extremely ___sharp mind.

一个敏锐的侦探能注意到别人忽略的线索。

A ___sharp detective can notice clues others miss.