_______ for the free ticket, I would not have gone to see film so often.
A、IfitisnotC
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。
By"languageacquisitionisprimarilytheacquistionofthegrammaticalsystemoflanguage",linguistsmeanthat______.
EmpiricalstudiesshowthattheprocessofSLAisaprocessofconstructingandmodifyingrulesofcommunication.
Iwaswritingareportlastnight;________Iwouldnothavestayeduplate.
This is an important problem _______ too few social scientists have researched.
Iaskedhimto________meafewminutessothatwecouldgooveralltheproblems.
