为什么要这么绝对地认为二者可以相互替换呢。I don't want to answer that question. 你能用in answer to去替换to answer 吗？一个是介词短语，一个是不定式，二者怎么可以随便替换呢？

蓸老师,例如这两句话 Write a complete sentence in answer to each question. In answer to these questions I either nodded or made strange noises. in answer to替换成to answer 吧？

你只能说在特定的情况下，比如作状语时，二个结构可以表示近似的意义，但你不能说二者相等。严格讲，不定式为目的状语，in answer to为时间状语，即在回答...的过程中。

thank you very much !