_______ for the free ticket, I would not have gone to see film so often.
C
从本题后半句可以看出这是一个与过去事实相反的虚拟条件句，从句中的动词要用“had+过去分词”，如果将if省略，had要位于主语之前，构成倒装句，故本题的答案是C。Haditnotbeenforthefreeticket=Ifithadnotbeenforthefreeticket。
If payment is not received, legal action will be our only ________.
Lying under the skull, the human brain contains an average of ten billion nerve cells called ______.
If you are walking away from a clock tower ，you will hear the ticking of the clock fade to a point ________ it cannot be heard.