It was not until she had finished all her work_______home tired

A．did she return 　　　　　　　

B．that she returned

C．when she returned

D．that did she return

请在下列①、②2小题中任选一题作答，若两题都作答则以第一题计分．

①日常生活中我们接触到的水有硬水和软水．请写出一种确定你某次使用的水是硬水还是软水的方法，要求有操作步骤、现象、结论．

②写出2种造成水污染的污染源，并写出一件你可以做到的、有利于防止水污染的事例．