In answer to these questions I either nodded or made strange

楼上的朋友对 answer 与 answering 的用法已说得很清楚,我就不重复了.不过,您的提问‘为什么用answer而不用answering’,还没得到具体的回答.
其实,两者是有点区别的.
In answer to these questions I either nodded or made strange noises.作为名词,句子后段表达的是回答的内容,这些问题所得到的回答是点头和怪声.
In answering these questions,he appeared evasive.作为动词,这里句子后段表述的是回答的态度或动作.