有关窗宽的论述，正确的是（）

A.窗宽决定显示CT值范围的大小

B.窗宽加大，可提高图像中低密度组织对比

C.组织的CT值大于窗宽规定范围时呈白色

D.窗宽除以16，等于每个灰阶包含的CT值

E.调剂窗宽可以改变图像的密度差

There is nothing in this world constant but inconstancy.--SWIFT Project after project designs a set of algorithms and then plunges into construction of customer-deliverable software on a schedule that demands delivery of the first thing built. In most projects, the first system built is (1) usable. It may be too slow, too big,awkward to use, or all three. There is no (2)   but to start again, smarting but smarter, and build a redesigned version in which these problems are solved. The discard and  (3) maybe done in one lump, or it may be done piece-by-piece. But all large-system experience shows that it will be done. Where a new system concept or new technology is used, one has to build a system to throw away, for even the best planning is not so omniscient（全知的）as to get it right the first time. The management question, therefore, is not whether to build a pilot system and throw it away. You will do that. The only question is whether to plan in advance to build a (4)  ,or to promise to deliver the throwaway to customers. Seen this way, the answer is much clearer. Delivering that throwaway to customers buys time, but it does so only at the (5)  of agony（极大痛苦）for the user, distraction for the builders while they do the redesign, and a bad reputation for the product that the best redesign will find hard to live down.. Hence plan to throw one away; you will, anyhow.

空白（5）处应选择（）

A.worth

B.value

C.cost

D.invaluable