If a PHP expert wants to replace multiple keywords in str_replace, how should he write the first parameter?

str_replace(find,replace,string,count)
How to write if find is several keywords

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str_replace(find,replace,string,count)
How to write if find is several keywords

<code>str_replace(['a','b','c'],'a',$str);//a或b或c都替换成a
str_replace(['a','b','c'],['d','e','f'],$str);//a->d b->e c->f</code>