(as) sharp as a tack
very intelligent.
He may be old in years, but he's still as sharp as a tack and knows what he's talking about.
英语词组固定搭配大全包含18674条英汉双解词组，基本涵盖了全部常用英文词组、短语的翻译及用法，是英语学习的有利工具。