哪一类生态系统不完全属于自然生态系统 [ ]

A．农田生态系统   

B．鱼塘生态系统   

C．河流生态系统   

D．雪山生态系统

The company should establish procedures to ensure that（）related to safety and protection of the environment are given proper familiarization with their duties.Instructions which are essential to be provided prior to sailing should be identified,documented and given.

A.New personnel

B.Personnel transferred to new assignments

C.All crewmembers

D.New personnel and Personnel transferred to new assignments