A:y=x+5
B:y=x+10
C:y=﹣x+5
D:y=﹣x+10
声呐在海洋勘察和军事方面都是一种重要的仪器.从知识上看,它是一种能定向发射和接受____(选填“超声波”或“次声波”)的设备.
When the meeting was ________, they all ________ to their feet and left.