I prefer usually challenging questions, while I may spend some time on easier ones trying to explain something that used to be difficult for me.
My preference goes to algorithms, and C, a language that I've liked and known for a long time, while I like also to visit server fault and its many interesting and challenging system, DB, nginx, ... questions and answers.
Linux has been my working environment for almost 10 years. And a (few) Mac for leisure.
Keeping a low profile.
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