A:Warned; accompanied
B:Having warned; accompanying
C:Warning; accompanying
D:Having been warned; accompanying
This box is_______ that one.
下面是小娜和张婷同学做“探究响度与什么因素有关”的实验,回答下列问题:
将系在细线上的乒乓球轻触正在发声的音叉.观察到乒乓球被弹开的现象 (如图所示).