问一道36套里EX24的一道题。。

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Because of its accuracy in outlining the Earth's subsurface, the seismic-reflection method remains the most important tool in the search for petroleum reserves. In field practice, a subsurface is mapped by line arranging a series of wave-train sources, such as small dynamite explosions, in a grid pattern. As each source is activated, it generates a wave train that moves downward at a speed determined uniquely by the rock's elastic characteristics. As rock interfaces are crossed, the elastic characteristics encountered generally change abruptly, which causes part of the energy to be reflected back to the surface, where it is recorded by seismic instruments. The seismic records must be processed to correct for positional differences between the source and the receiver, for unrelated wave trains, and for multiple reflections from the rock interfaces. Then the data acquired at each of the specific source locations are combined to generate a physical profile of the subsurface, which can eventually be used to select targets for drilling.

5. It can be inferred from the passage that the seismic-
reflection method would be likely to yield an inaccu-
rate physical profile of the subsurface in which of
the following circumstances?
(A) If the speed at which the wave train moved
downward changed
(B) If the receiver were not positioned directly at
the wave-train source
(C) If the rock on one side of a rock interface had
similar elastic characteristics to those of the
rock on the other side
(D) If the seismic records obtained for the different
sources in a grid were highly similar to each other
(E) If there were no petroleum deposits beneath the
area defined by the grid of wave-train sources

正确答案是C，请问如何甄别C和D？我选的D。。。
多谢各位！

竹林中人

for unrelated wave trains，这里主要看这句吧，如果波是相关的相联系的，那么就会出现误差，而波是由石头的弹性特征决定的，如果两个之间的弹性特征相同，那么最终的结果肯定是不准确的。

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竹林中人 发表于 2013-8-21 19:02
for unrelated wave trains，这里主要看这句吧，如果波是相关的相联系的，那么就会出现误差，而波是由石头 ...

原文越看越糊涂，斑竹可以费心解释一下大致机制吗？

竹林中人

面无表情 发表于 2013-8-21 20:00
原文越看越糊涂，斑竹可以费心解释一下大致机制吗？

我大概的说下，一地方被激发了，产生波，波的传播速度是由石头的弹性特征唯一决定的，当相接的石头的弹性系数突然改变的时候，会在石头上产生反射，这样接收到反射到的波之后，通过计算可以描绘出地下的物理特征。所以必须出现石头的弹性系数发生突变，否则很相近的话，会产生很大的误差

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竹林中人 发表于 2013-8-21 20:16
我大概的说下，一地方被激发了，产生波，波的传播速度是由石头的弹性特征唯一决定的，当相接的石头的弹性 ...

嗯好像懂了，意思是这样产生的波会比较少，所以误差大对吧。。。但是D为什么不对呢？TAT

竹林中人

面无表情 发表于 2013-8-21 20:29
嗯好像懂了，意思是这样产生的波会比较少，所以误差大对吧。。。但是D为什么不对呢？TAT ...

similar指的不够具体吧，如果弹性系数不一样，其他的一样的话，还是可以啊