单选题 21. ______ it was not his responsibility to do that, he said he would help.

【正确答案】 A

【答案解析】[考点] 词义辨析
although：尽管，虽然；if：如果；since：自从，既然；unless：如果不，除非。根据句意可知，选A。
尽管做那件事并不是他的职责所在，他仍说他会帮忙。