语法与词汇 21.In the late 1800's Ellen Richards, began work in the new field of "sanitary science" which was concerned with waste removal, water purification and .
【正确答案】 B
【答案解析】本题考查句子结构。分析句子可知，which引导定语从句，修饰“sanitary science(公共卫生学)”，其中and连接三个并列名词词组，故所填的词组应与waste removal和water purification的结构一致，故答案为[B]项。