After going into the concert hall, the mother ________ a friend and went over to greet him.

A．searched

B．knew

C．realized

D．spotted

巡航时，航空活塞发动机最佳功率混合比是满足下列哪种条件的油/气比（）？

A.使气缸头温度最低；

B.对给定的油门位置，可获得相应的最大功率；

C.使排气温度过高。