lsat 14 ,sec2 ,18/19

Questions 18 – 19
Each year, an official estimate of the stock of cod in the Grand Banks is announced. This estimate is obtained by averaging two separate estimates of how many cod are available, one based on the number of cod caught by research vessels during a once-yearly sampling of the area and the other on the average number of tons of cod caught by various commercial vessels per unit of fishing effort expended there in the past year – a unit of fishing effort being one kilometer of net set out in the water for one hour. In previous decades, the two estimates usually agreed closely. However, for the last decade the estimate based on commercial tonnage has been increasing markedly, by about the same amount as the sampling based estimate has been decreasing.
18. If the statements in the passage are true, which one of the following is most strongly supported by them?
(A) Last year’s official estimate was probably not much different from the official estimate ten years ago
(B) The number of commercial vessels fishing for cod in the Grand Banks has increased substantially over the past decade
(C) The sampling-based estimate is more accurate than the estimate based on commercial tonnage in that the data on which it relies is less likely to be inaccurate
(D) The once-yearly sampling by research vessels should be used as the sole basis for arriving at the official estimate of the stock of cod
(E) Twenty years ago, the overall stock of cod in the Grand Banks was officially estimated to be much larger than it is estimated to be today

19. Which one of the following, if true, most helps to account for the growing discrepancy between the estimate based on commercial tonnage and the research-based estimate?
(A) Fishing vessels often exceed their fishing quotas for cod and therefore often underreport the number of tons of cod that they catch
(B) More survey vessels are now involved in the yearly sampling effort than were involved 10 years ago
(C) Improvements in technology over the last 10 years have allowed commercial fishing vessels to locate and catch large schools of cod more easily
(D) Survey vessels count only those cod caught during a 30-day survey period, whereas commercial dishing vessels report all cod caught during the course of a year
(E) Because of past overfishing of cod, fewer fishing vessels now catch the maximum tonnage of cod each vessel is allowed by law to catch

这两道题我实在看不懂题目，做错了，18题不理解为什么是a

Q18: (A)

"for the last decade the estimate based on commercial tonnage has been increasing markedly, by about the same amount as the sampling based estimate has been decreasing."

One figure increased, and the other decreased, at about the same amount

Therefore, the average of the two figures, which is the "estimate", should not show big difference from previous estimate.

Q19: my answer is (c):

Technology improvements allowed commercial fishing vessels to catch more cod. Since commercial estimate  is "the average number of tons of cod caught by various commercial vessels per unit of fishing effort expended there in the past year", the commercial estimate increased a lot.

斑竹我看不懂题目

大意为：平均两组数据来估计Cod鱼的存量。一组数据是研究船每年取样时捕的鱼量，一组是平均去年各商业船的 fishing effort expended 所捕的鱼量（每小时每公里撒网所捕的鱼）。过去几十年，两组数据较吻合。但在过去的十年，商业船的数据明显增加，而取样船的数据等数量（和商业船）减少。

Q18如chelsea版主所说。Q19因为计算单位是每小时捕的鱼量，如果如C所说鱼更易定位和捕捉，则单位时间捕的鱼更多，所以能解释商业船捕鱼量的增加。

18 CC。谢谢

19不明白：为什么题目要解释差距增大的原因，而答案之解释了增大的一方没有解释变小的那方的原因？？？

ＴＨＸ