Hardly ______ his speech ______ the audience started cheering.

A．did he finish; than

B．does he finish; before

C．has he finished; while

D．had he finished; when

端午节期间，郑能随父母到山区爬山，他向着远处的山崖大喊一声，约1.6s听到回声，他们距山崖大约   m，声速按340m/s计算。声音在空气中以     的形式传播。