题目解析:
题干提问“淤泥怎样影响黄河?”
定位第2段第2句 It is generally understood that the river, running through a vast area where the fine and porous soil accounts for the large silt content in its current, has a constant tendency to clog its own course and cause dikes to break and enormous inundations to occur.
即淤泥 silt 会堵住河道 clog its own course。
故选 B。