If I ____ you, I would not have done that.
What has happened to the subjunctive in English? Here, at least, it's an option ("were"), but I would have guessed that the question would have asked for choosing between "were" and "was." I almost never hear someone use "were." For example, "If I were leaving tomorrow, I would be packing right now." Most people seem to use "was." Grrr.