What does the author mean when he writes "when twins grow up together they constantly have the other twin there with them, making them really close to one another and social with each other?

there are number of topics. you can pick any one of these topics:

linux &   windowsdocumentary & fictionextroverts & introvertsdoctor and teacherfootball and basketballvegetarians & non-vegetarians.european history and us history

is basically a good source of getting and others by what you know for example if someone asked a question and you know the answer you could answer it and get some points or if you need on a question you could make a post about it and wait till someone answers it or just look up the question and see if someone else has asked about it