Tired ____ he was, we decided not to disturb him.
A. though B. although C. as D. like(全国研考)
谢振元教授主编的《研究生入学考试英语复习指南(1998)》(中国人民大学出版社, 1997, p.29)对上题作了如下解答：
“形容词(或过去分词) + as + 主语 + 谓语动词(或连系动词) = Although + 主语 + 谓语动词(连系动词) + 形容词(或过去分词)。例如: Diligent as he was (= Although he was diligent), he failed in the English final exam.”
上题中的Tired as he was 果真像该书所解答的那样等于 Although he was tired(尽管他很
疲劳)吗?
应当搞清楚，倒装语序的 as 从句既可以表让步，也可以表原因。从句子的内容来看，试题中的从句 Tired as he was，只能是原因状语从句，而不可能是让步状语从句。因为从句对于主句显然是原因关系：由于他很疲劳，我们决定不去打扰他。
请分析下列实例：
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Tired as they were, they went to bed as soon as they came back. (CGEL) 他们由于很累，一回到家里就上床睡觉了。
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Experienced as he is in contrast to his colleagues, he can deal with any difficult situation. 由于他跟同事们相比很有经验，所以他能对付任何困难的局面。
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Unaccustomed as I am to public speaking, I beg your indulgence for my few inelegant words. 由于我不习惯于发表演说，有些话讲得不大得体敬请原谅。
只有在让步状语从句里,这种特殊语序中的 as 才是可以用 though 来替换的:
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Tired as they were( =Tired though they were), Jurgis and Ona sat up late. (Sinclair) 尽管朱尔金斯和奥纳很疲惫, 但是他们很晚才睡。
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Poor as he was( = Poor though he was), he was honest. (Eckersley) 虽然他很穷,但是很诚实。
(参见 though )