问道大全里的语法题！！！

traviszhu

1.    Coronary angiography, a sophisticated method for diagnosing coronary disease involving the introduction of a dye into the arteries of the heart, is now administered selectively, because it uses x-rays to observe cardiac function.
(A) for diagnosing coronary disease involving the introduction of a dye into the arteries of the heart, is now administered selectively, because it uses
(B) for diagnosing coronary disease involving the introduction of a dye into the arteries of heart, is now administered selectively, because of using
(C) for diagnosing coronary disease, involves the introduction of dye into the arteries of the heart and is now administered selectively, because it uses
(D) to diagnose coronary disease that involves the introduction of a dye into the arteries of the heart, is now administered selectively, because it uses
(E) to diagnose coronary disease involving the introduction of a dye into the arteries of the heart, which is now administered selectively, uses
答案是C，这个"for"怎么解释啊

Aleonid

for用来修饰method，表示一种能力。不定时在此表示目的，有强调动作的感觉。所以并不是所有的地方都用不定式。