参考答案：No matter how(they are)frequently performed/However frequently(they are)performed

解析： 本题考查对no matter引导状语从句的掌握。No matter经常与特殊疑问词连用，引导让步状语从句，本句中frequently“频繁”是一个副词，修饰动词perform，故应该用特殊疑问词how来修饰副词frequently；而the works与perform之间是被动的关系，故状语从句应该采用被动语态。而且，由于从句主语与主句主语一致，因此可将they are省略。另外，no matter how frequently也可．以用however frequently来替换。