求教GWD 6-11，討論區找不到

Q11:

In 1992 outlaw fishing boats began illegally harvesting lobsters from the territorial waters of the country of Belukia.  Soon after, the annual tonnage of lobster legally harvested in Belukian waters began declining; in 1996, despite there being no reduction in the level of legal lobster fishing activity, the local catch was 9,000 tons below pre-1992 levels.  It is therefore highly likely that the outlaw fishing boats harvested about 9,000 tons of lobster illegally that year.

Which of the following is an assumption on which the argument depends?

1. The illegal lobster harvesting was not so extensive that the population of catchable lobsters in Belukia’s territorial waters had sharply declined by 1996.
2. The average annual lobster catch, in tons, of an outlaw fishing boat has increased steadily since 1992.
3. Outlaw fishing boats do not, as a group, harvest more lobsters than do licensed lobster-fishing boats.
4. The annual legal lobster harvest in Belukia in 1996 was not significantly less than 9,000 tons.
5. A significant proportion of Belukia’s operators of licensed lobster-fishing boats went out of business between 1992 and 1996.

答案是A，為什麼呢？理不出思路...

论据：合法捕捉少了9000吨，结论：非法捕捉了9000吨。

这两者有什么关系呢？

选项not+weaken：非法捕捉不会extensive到使得整体数量减少的地步。

如果非法捕捉会是整体数量减少的话，那么整体数量=合法+非法，不能得出非法捕捉了9000吨的结论。