One CR from June JJ??

Could someone tell me what the answer is for the following CR from June JJ?? Thanks!!

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Lead left in soil can be traced years past. Lead comes from car's waste tail gas. Soil nearby highway roads has higher trace of lead if more cars are on the highway. In 1970-1980, lead was added in car's gasoline, so we can conclude that the highway traffic was busy at that time if soil tested there contains more lead.

commit which following mistake?

A. take one probable cause as the only cause for a result.

C. take what is necessary to a conclusion as what is sufficient to that conclusion.(6/21/2004)

I think B is better.

premise: more cars on the highway ——>higer trace of lead.  "Higer trace of lead" is necessary to "more cars on the highway".

conclusion: higher trace of lead——>more cars on the highway. "more cars on the highway" is sufficient to "Higer trace of lead".

Therefore, the mistake committed is to take what is necessary to a conclusion as what is sufficient to that conclusion.

Discussion welcome.

I still think A is better, since "more cars on the road" is only one possible reason for high lead in the soil. Thus "more cars on the road" is not neccessary for the result. It might be caused by other reasons.

Any other opinion?

Agree B is right.  but a little correction.

conclusion: higher trace of lead——>more cars on the highway   "Higer trace of lead" is   sufficient to " more cars on the highway'.

A is necessary to B:  B-->A       A is sufficient to B: A-->B