A standard one. Replacement during the first year if all rules for proper use have been followed.
有一个原则,如果在一年内符合各种使用规定,就可更换。
Every solid object will reflect a sound, varying according to the size and nature of the object.
任何固体者反射声音,反射的声音因物体的大小和性质的不同而不同。