gwd1-12这句话是什么意思啊

kevinjpcn

gwd1-12这句话是什么意思啊

The author mentions the "aftermath of the Mount Saint Helens eruption" most likely in order to
A  provide an example of the process that allows the repopulation of rivers whose indigenous salmon population has become extinct
B  indicate the extent to which the disturbance of salmon habitat by human activity in one stream might affect the genetic structure of salmon populations elsewhere
C  provide a standard of comparison against which the impact of human activity on the gene flow among salmon populations should be measured
D  show how salmons' homing instinct can be impaired as a result of severe environmental degradation of their natal streams
E  show why straying rates in salmon populations remain generally low except when spawning streams suffer severe environmental disturbance




其中的C选项的which指代什么啊？怎么翻译啊

麻烦大牛指点一下啊

Elfy

impact of human activity 的影响可以通过aftermath of the Mount Saint Helens eruption的数据来衡量

kevinjpcn

Elfy，谢谢。
我明白了。
measure against是个习惯用语，表示以...来测量。
句中的against which 的which指代standard，也就是measure against a standard of comparison
也就是aftermath of the Mount Saint Helens eruption作为了一个比较的标准（a standard of comparison)。我以前认为which指代comparison所以没有理解这个句子，其实comparison跟在介词of的后面，不能被which指代的啊。
举例：
What star serves as a standard of comparison against which the brightness of other star is measured?

http://wiki.answers.com/Q/What_star_serves_as_a_standard_of_comparison_against_which_the_brightness_of_other_star_is_measured

断了的弦

should be measured 的主语是什么啊？这是一句虚拟语气吗？