答案：C

题目分析：考查虚拟语气：根据主句中的would not have gone 可知，这是与过去事实相反的虚拟语气。结构如下：主句：主语+would/should/could/might+have done+其他

从句：if+主语+had+过去分词+其他，还可以构成倒装：去掉if,把had提前。所以，上面的句子应该是：If it had not been for the free tickets,I would not have gone to the films so often.

写成倒装就是：Had it not been for the free tickets,I would not have gone to the films so often。选C。

点评：if的非真实条件句，可以省略if，提前were，should，had，这是一种特殊的表达方式，做题时要结合主句进行判断。