材料： Coastal conditions The area described in the volume presents the mariner with a generally adverse combination of navigational factors which are outline below． Local Topography．The Dover Strait is shallow and only is 18 miles wide at its narrowest point．Passage through the strait is further constricted by a series of narrow banks，running NE-SW．The seabed is also littered with wrecks． Natural Conditions．There are strong tidal streams in the strait．Sea level may differ from that predicted and in particular may be lower than expected due to negative tidal surges．The area is also subject to gales and poor visibility． Risk of Collision．There is a high risk of collision caused by the density of vessel traffic on passage through the strait，including deep-draught vessels，and crossing traffic，including ferries and high speed craft． Mine danger area There are two areas off the N coast of France，which remain dangerous because of mines lied in the war of 1939-1945．Due to the lapse of time the risk to surface navigation is now considered to be no more dangerous than that the ordinary risks of navigation but a very real risk still exists with regard to anchoring，fishing or any form. submarine or seabed activity． 问题： The crossing traffic in the Dover Strait is probably running ________． A.NE-SW B.SE-NW C.N-S D.E-W It is implied in the passage that ________．A.mine is not a danger to surface navigation in Dover Strait B.the width of Dover Strait is not so narrow C.the natural conditions in Dover Strait are too serous D.collision with deep-draught vessels or ferries or high speed craft in Dover Strait is hardly avoidable According to the passage，the risk of collision in the Dover Strait is caused by ________．A.gales and poor visibility B.a series of narrow banks C.the density of vessel traffic on passage through the strait and crossing traffic D.a generally adverse combination of navigational factors It is inferred that ________．A.although the tidal streams in Dover Strait is strong，there were few ships sunk in it B.most of the wrecks in Dover Strait were deep-draught vessels，ferries and high speed craft C.the wrecks are not dangers to surface navigation D.there were many ships sunk in Dover Strait