大全-C-20

20.   Since the invention of digital readout, machine designers have rushed to replace conventional dials and gauges with digital units. Yet the digital gauge has drawbacks in some situations. Since it presents an exact numeric value, it must be decoded and analyzed by a human operator; its meaning cannot be read in an instantaneous scanning. An analog dial or gauge can be marked with red to alert the operator when a value is entering a danger zone; a digital gauge cannot. And it is difficult to tell whether a digital readout is increasing or decreasing over time, while the up or down movement of a pointer on an analog gauge can be quickly and easily observed.

The author of the passage above would probably recommend the use of digital gauge in cases when

I.     warning of a sudden rise or fall in value is needed

II.    an operator must read and interpret several gauges within a few seconds

III.   a precise numeric value is essential

(A) I only

(B) III only

(C) I and III only

(D) II and III only（B）

(E) I, II, and III

为什么不能选D呢,请NN指教

I为何不对啊? 文中说了跟传统的刻度盘的量具比,电子读数的量具有两个缺点:1)因为它显示的是精确的数值,所以它必须由人来解码和分析,它数值所代表的意思就不能即时地被读懂. 2)传统的量具只要指针数值一进入危险区,操作员就知道了,而电子的不行.3)很难预测电子读数随时间的变动(上升或下降)趋势,而传统的量具却可以很快且很容易从指针的上下波动来预测变动趋势.

然后问题是怎么样电子读数的量具才能被推荐使用.我觉得解题思路应该解决电子读数量具的缺点入手啊?我怎么觉得除了I别的答案都不对呀? 还是我的思路有问题?

欢迎讨论!

I. warning of a sudden rise or fall in value is needed

part of the conclusion: 

part of the conclusion: 

don't you see that I and the conclusion are talking about the same thing in terms of having difficulties of judging the direction of sudden change?

don't you see that I and the conclusion are talking about the same thing in terms of having difficulties of judging the direction of sudden change?

in order to understand the text , you'd better know the fallowing words :

dials刻度盘and gauges标尺