[大全]2-20

[vitality]

Blood banks will shortly start to screen all donors for NANB hepatitis. Although the new screening tests are estimated to disqualify up t o5 percent of all prospective blood donors, they will still miss two-thirds of donors carrying NANB hepatitis. Therefore, about 10 percent of actual donors will still suppy NANB-contaminated blood.

20. Which of the following inferences about the consequences of
instituting the new tests is best supported by the passage above?

(A) The incidence of new cases of NANB hepatitis is likely to go up by 10
percent.

(B) Donations made by patients specifically for their own use are likely to
become less frequent.

(C) The demand for blood from blood bank is likely to fluctuate more
strongly.

(D) The blood supplies available from blood banks are likely to go down.

(E) The number of prospective first-time donors is likely to go up by 5
percent

雖然我是選(D) 正確答案 不過總覺得不知道改怎麼解釋較好

一下問了好幾題 感謝各位的解答!!!

[DARY]

Blood banks will shortly start to screen all donors for NANB hepatitis. Although the new screening tests are estimated to disqualify up t o5 percent of all prospective blood donors, they will still miss two-thirds of donors carrying NANB hepatitis. Therefore, about 10 percent of actual donors will still suppy NANB-contaminated blood.

20. Which of the following inferences about the consequences of
instituting the new tests is best supported by the passage above?

(A) The incidence of new cases of NANB hepatitis is likely to go up by 10
percent.

(B) Donations made by patients specifically for their own use are likely to
become less frequent.

(C) The demand for blood from blood bank is likely to fluctuate more
strongly.

(D) The blood supplies available from blood banks are likely to go down.

(E) The number of prospective first-time donors is likely to go up by 5
percent

雖然我是選(D) 正確答案 不過總覺得不知道改怎麼解釋較好

一下問了好幾題 感謝各位的解答!!!

事實:
新的監測機制可以篩掉5%不合格的人
但也篩掉了2/3合格的人

想像:
這些真正合格而且有捐到血人的看到即使自己是合格的
但能成功捐血的機率竟只有三分之一

結論:
真正合格而且有捐到血人的只有10%想再來捐血

推論:(即答案)
血(NANB-contaminated blood)的獲得將會愈來愈少
當然也有新的捐血者在未來出現；但只有在新的捐血者爆增，才能在1/3的成功率下合格且捐到血的人比之前來得多
所以答案裡用了be likely to....

[dibert8]

每一個第一次的捐血者都有5%的機率被刷掉,或者每一批第一次的捐血者都會被刷掉5%,合格的捐血者就越來越少,因此造成供給不足.
=> (D)

(A) 每一批捐血的人有5%他們的血會被篩選掉,即100人之中,有95人的血會被拿去用.而其中10人捐的血是帶 NANB hepatitis.這些人捐幾帶血不知道,因此無法由此推出因輸血而感染的比例.
(B) 如果知道會被感染,保險的話,自己輸自己的血應該比較安全吧.
(C) (E) 無法作此推論也