A chock is a（）.

A.deck fitting used to secured mooring lines

B.casting fitting at the side of a weatherdeck, used as a fairlead

C.sharp block of wood used to support hygroscopic cargo

D.smoke pipe for the galley stove

采用DMA方式，在存储器与I/O设备间进行数据传输；对于PC来说，数据的传送要经过( )。

A．CPU

B．DMA通道

C．系统总线

D．外部总线