【泣血求助】白勇P135-31题-【关于举例的成分省略】

白勇P135-31题
1. Researchers have questioned the use of costly and experimental diagnostic tests to identify food allergies, such as milk, that supposedly disrupt normal behavior.
A. to identify food allergies, such as
C. to identify food allergies, such as to
该题答案选C，但这里为什么要加个to呢？
后面解释说是举例的省略。。。我的问题是，举例（such as)是不是像定从或者分词那样就近修饰名词？ 有没有可能是跳跃修饰，比如上面有没有可能是...such as a test to milk..
这里所说的省略的一般公理是什么？什么样的举例成分是可以省略的？