What are the rules for the Sports Center We can listen to music ________ we can’t eat food there．

31．Every solid object______reflect a sound，varying according to the size and nature of the object．

.If a computer crashes, you will lose the file you _________unless you save it regularly

The lower room was in darkness, but by _____ his way he found the bag.

This time last year I paid a visit______Shandong which is 5000 kilometers _____