如图是人体肾单位结构示意图,请据图回答。
某物体发出的声音在空气中的波长为1 m,波速为340 m/s,在海水中的波长为4.5 m,此物体在海面上发出的声音经0.5 s听到回声,则海水深为____ m.
Good news! We'll have ____ one-day holiday in order to celebrate the 70th annzversary(纪念日)of the victory in World War II.