13．_______ someone throws in some rubbish，it produces a piece of music．

12．He hurried off _______ he was able to catch the early bus．

11．Tom ran _______ fast _______ I couldn't keep up with him．

10．We won't go home _______ we finish our work．

9．We are never late for class _______ the new teacher is strict with us．

8．The girl has studied in the town _______ her family moved here．

7．I'll tell her about the important news _______ I see her．

6．Wash your hands _______ you eat something．

5．We usually clean the classroom _______ class is over．

4．Could you tell me _______ there is any water left？