asdfghjklasdfghj , this is not an iron-clad rule. We do want to avoid gratuitous commas. For instance, it's wrong to write "I like to sing, and dance." However, there are some cases in which the sentence is potentially complicated or confusing enough that a comma is warranted. There are official GMAT SC questions that do this, even in places where I personally would not choose to use a comma. Here's an example: https://gmatclub.com/forum/covering-71-
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