User talk:Sanam kheradmand

Recent edit to Progressive collapse
Hello, and welcome to Wikipedia. I noticed that you made a change to an article, Progressive collapse, but you didn't provide a reliable source. It's been removed for now, but if you'd like to include a citation and re-add it, please do so! If you need guidance on referencing, please see the referencing for beginners tutorial, or if you think I made a mistake, you can leave me a message on my talk page. Thank you! Materialscientist (talk) 12:55, 22 January 2017 (UTC)