Historian: We can learn about the medical history of individuals through chemical analysis of their hair. It is likely, for example, that Isaac Newton’s psychological problems were due to mercury poisoning; traces of mercury were found in his hair. Analysis is now being done on a lock of Beethoven’s hair. Although no convincing argument has shown that Beethoven ever had a venereal disease, some people hypothesize that venereal disease caused his deafness. Since mercury was commonly ingested in Beethoven’s time to treat venereal disease, if researchers find a trace of mercury in his hair, we can conclude that this hypothesis is correct.

Which one of the following is an assumption on which the historian’s argument depends?

A. None of the mercury introduced into the body can be eliminated.

B. Some people in Beethoven’s time did not ingest mercury.

C. Mercury is an effective treatment for venereal disease.

D. Mercury poisoning can cause deafness in people with venereal disease.

E. Beethoven suffered from psychological problems of the same severity as LACE>NewtonLACE>’s.

本題答案是B 可否請高手幫忙說明一下!! 俺實在是看不懂哩~~~

最后几句“虽然没有令人信服的证据表明Beethoven曾经得过venereal disease，但是一些人猜想是venereal disease这种病导致Beethoven耳聋的。这是因为在Beethoven时代通常用水银治疗venereal disease这种病。因此，如果研究人员在他的头发中检测到含有水银，那么我们就可以认为那些人的猜想是正确的。”

其中关键一句是‘ 在Beethoven时代通常用水银治疗venereal disease这种病’，只有患有venereal disease病的人才会摄入水银。如果那个时代的人都摄入水银，那么那个时代的任何人的头发中都会含有水银了，这样即使在Beethoven头发中发现水银，也就不能说明什么了。

因此 B选项只有部分人（特指患有venereal disease这种病的人）才会摄入水银 是必须的假设