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碰到一道题
The yield of natural gas from Norway's Troll gas field is expected to increase annually until the year 2005 and then to stabilize at six billion cubic feet a day, which will allow such an extraction rate at least for 50 years' production.
A.2005 and then to stabilize at six billion cubic feet a day, which will allow such an extraction rate at least for
B.2005 and then to stabilize at six billion cubic feet a day, an extraction rate that will allow at least
C.2005 and then stabilizing at six billion cubic feet a day, with such an extraction rate at the least allowing
D.2005, then stabilizing at six billion cubic feet a day, allowing such an extraction rate for at least
E.2005, then stabilizing at six billion cubic feet a day, which will allow such an extraction rate for at least
这道题通过判断平行结构，排除了除B外的所有选项，虽然是做对了，但是不太理解B选项的an extraction rate that will allow at least算是什么成分？应该不算独立主格作伴随修饰吧？？如果不是的话，除了语法笔记上写的独立主格，分词短语，形容词短语，单个形容词这些成分以外，还有哪些是能够做伴随状语的呢？？烦请NN能列举，帮助小弟总结，谢谢！