You can put as many practice areas on your website as you want. It doesn’t matter because Google will only show the content the searcher queried for, but in article pages, you should have different pages for different practice areas because Google is able to algorithmically detect keywords of a website and takes the searcher to the a page with relevant content.
On the other hand, if you do have separate websites specific to two different practice areas, you will do a little bit better but two websites will cost you more money.
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