If you're confused about that versus which, don't feel bad. It's one of the most common topics people ask me about. I used to work as a technical writer, and I'd often edit documents in which people used the wrong word. More than once, I'd put in the right word, only to have clients change a perfectly fine that to a which and send it back to me. In fact, having a client try to overrule my correction of a which to a that was one of the things that pushed me over the edge and made me start the Grammar Girl podcast: http://grammar.quickanddirtytips.com/which-versus-that.aspx
More grammar girl`s tips for better writing: http://vk.com/audios-17650165?album_id=37377016
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