After suffering a heart attack, Michael Jackson was pronounced dead, ___ a tragic end to the world’s most popular entertainer.

A．having marked

B．to mark

C．marked

D．marking

起落架系统中的反向活门是（）

A、由侧撑杆机械作动的

B、确保在起落架运动过程中确保主起落架舱门打开

C、由主起落架上锁机构机械作动

D、A和B