这题那位看懂了，请解释一下好吗？

frankzhiwei

The cause of the wreck ofthe ship Edmund Fitzgeraid in a severe storm on lake Superior is still unknown, when the sunken wreckage of the vessel was found, searchers discovered thehull in two pieces lying close together, The storm’s violent waves would havecaused separate pieces floating even briefly on the surface to drift apart.Therefore, the breakup of the null can be ruled out as the cause of thesinking.
Which of the following isan assumption on which the argument depends?
A.       Ships as large as the Edmund Fitzgerald rarely sink exceptin the most violent weather.
B.        Under water currents at the time of the storm did not movethe separated pieces of the hull together again.
C.       Pieces of the hull would have sunk more quickly than theintact hull would have
D.       The waves of the storm were not violent enough to havecaused the breakup
E.        If the ship broke up before sinking , the pieces of thehull would not have remained on the surface for very long










真没看懂，答案是B，求解释~

sdcar2010

Necessary assumption.  Use negation!

When you negate B, what you get is that the current can put the two pieces together AFTER the ship broke up. If this is true, then the conclusion of the argument "the breakup of the null can be ruled out as the cause of the sinking" won't hold because the conclusion is based on the assumption that if the ship broke into two pieces before sinking, the two pieces would be drifted apart and landed in the bottom of the lake far apart. However, if B happens, even if originally the two piece were far apart, the current can put them back together AGAIN at the bottom.

Therefore, B is the necessary assumption of the argument.