雅思英文问题

题目

雅思英文问题
researchers have still to decide whether smell is one sense or two- one responding to odours proper and the other registering odourless chemicals in the air. 后半句 one responding to odours proper and the other registering odourless chemicals in the air proper在句子中做什么成分,registering在句子中做什么成分 和什么意思
而且为什么是动词ing形式

答案

后半句one……应该是解释说明two的意思,有哪两种气味
proper修饰odours,适宜的香味
registering修饰odourless chemicals,登记的无味的化学品