A:家弟.家妹
B:舍弟.舍妹
C:息弟.息妹
D:堂弟.弟妹
如右图所示,用悬挂着的乒乓球接触正在发声的音叉,乒乓球被弹开.这个实验是我们在学习《声现象》一章时经常做的实验,它说明了( )
In the future, working hours will be short. ________ people will have a long holiday.