修改一篇文章中的语法错误，并解释你的修改原因。


文本: "In his recent speech, the president has mentioned about the importance of clean energy."
修改后的文本: "In his recent speech, the president has mentioned the importance of clean energy."

修改原因: "mentioned about" 在该句中是无意义的用法，可以直接用"mentioned"代替。使用不当的词语会使语句的表达变得不清晰，容易产生歧义或误解。