Would you say "reading books "is" or "are"" [closed]
This is the sentence where it's used: "First of all reading books are important because it develops the mind."
In this case "reading books" is actually short-hand for "the act of reading books". If you substitute that into the given sentence, it's clear that you should use "is" rather than "are" as "the act" is singlular. As noted in the comments on the question, the use of "it" is also a clue.
First of all, [the act of] reading books is important because it develops the mind.