He suddenly saw Sue ---the room.He pushed.his way --the crow

across为“横穿”,与“道路”交叉形成“十字”.而through为在立体空间中的“穿过”.如：go through the forest“穿过森林”,go across the street “穿过大街”
房间的话,可以看做地面上横穿,不是立体的；人群肯定是立体空间都充满了障碍,用through
但是我觉得 房间用through也没问题.考试不会考这么模棱两可的题吧.
through表示“贯通、直穿、透过、穿过”的意思,即是从一头（边）贯穿到另一头（边）.
例The river runs through our city.这条河流经我们市.
He passed through the hall.他穿过大厅
across表示“横穿、横过、横渡、横跨”
例：I swam across the Changjiang River 20 years ago.
20年前我横渡了长江.
Look left and right before you go across the street.
过马路时要左右看.