[求助] 請教GWD 17-31

  The agreement, the first to formally require industrialized countries to cut emissions of gases linked to global warming, is a formal protocol by which 38 industrialized countries must reduce emissions of these gases by 2012 or face heavy penalties.
                                                                               
A. by which
B. for which
C. ubder which
D. such that
E. wherein

答案為C

看不出來介系詞是跟著哪個字的

這道題沒看到有人討論過

麻煩指點一下 謝謝!!

好似听说介词不是考试重点，这题先排除d和e,根据意思再排除b

by protocol和under protocol的话，考虑到protocol本身有政策法令的意思，under比较好把，不过这个也是事后诸葛的说法拉，呵呵