The boat is passing-----the bridge .A across B through C int

选B.意为船正在从桥下穿过.through意为从中穿过.
*across是从一头到另一头,比如go across the road,从马路的一边到另一边.
*into是进入内部,比如walk into the room.进入房子内部.然而船进入船洞不止要进去,还要 出来,则into肯定不合适.
* cross是动词,比如across the road.cross是across的介词形式.