需求曲线完全无弹性是指需求曲线：（）。 A.水平 B.垂直 C.倾斜45度角

城市道路的第一功能是（）。

A.交通的通道

B.组合型城市

C.工业经济的发展

D.组织城市的骨架

在投资项目经济评价中进行敏感性分析时，首先应确定分析指标。如果要分析产品价格波动对投资方案超额净收益的影响，可选用的分析指标是（）。

A．投资回收期

B．净现值

C．内部收益率

D．借款偿还期

缓冲区

When there is blood in the water, it is only natural that dorsal fins swirl around excitedly. Now that America’s housing market is ailing, predators have their sights on the country’s credit-card market. Analysts at Goldman Sachs reckon that credit-card losses could reach $ 99 billion if contagion spreads from subprime mortgages to other forms of consumer credit. Signs of strain are clearly visible. There are rises in both the charge-off and delinquency rates, which measure the share of balances that are uncollectable or more than 30 days late respectively. HSBC announced last month that it had taken a $1.4 billion charge in its American consumer-finance business, partly because of weakness among card borrowers.

It is too early to panic, though. Charge-offs and delinquencies are still low. According to Moody’s, a rating agency, the third-quarter delinquency rate of 3.89% was almost a full percentage point below the historical average. The deterioration in rates can be partly explained by technical factors. A change in America’s personal-bankruptcy laws in 2005 led to an abrupt fall in bankruptcy filings, which in turn account for a big chunk of credit-card losses ; the number of filings (and thus charge-off rates) would be rising again, whether or not overall conditions for borrowers were getting worse.

The industry also reports solid payment rates, which show how much of their debt consumers pay off each month. And confidence in credit-card asset-backed securities is pretty firm despite paralysis in other corners of structured finance. Dennis Moroney of Tower Group, a research firm, predicts that issuance volumes for 2007 will end up being 25% higher than last year.

Direct channels of infection between the subprime-mortgage crisis and the credit-card market certainly exist: consumers are likelier to load up on credit-card debt now that home- equity loans are drying up. But card issuers look at cash flow rather than asset values, so falling house prices do not necessarily trigger a change in borrowers’ creditworthiness. They may even work to issuers’ advantage. The incentives for consumers to keep paying the mortgage decrease if properties are worth less than the value of the loan; card debt rises higher up the list of repayment priorities as a result.

Card issuers are also able to respond much more swiftly and flexibly to stormier conditions than mortgage lenders are, by changing interest rates or altering credit limits. That should in theory reduce the risk of a rapid repricing of assets. "We are not going to wake up one day and totally revalue the loans," says Gary Perlin, Capital One’ s chief financial officer.

If a sudden subprime-style meltdown in the credit-card market is improbable, the risks of a sustained downturn are much more real. If lower house prices and a contraction in credit push America into recession, the industry will undoubtedly face a grimmer future. Keep watching for those dorsal fins.

According to the third paragraph, why would the number of bankruptcy filings be rising again （）

A. There is a change in America’s personal-bankruptcy laws

B. The charge-offs and delinquencies are still low

C. The influence of the personal-bankruptcy laws has been digested

D. The overall conditions for borrowers are getting worse

[背景材料]

某工程项目，采用钢筋混凝土剪力墙结构，施工顺序划分为基础工程、主体结构工程、机电安装工程和装饰工程四个施工阶段。

施工承包单位对该工程的施工方法进行了选择，拟采用以下施工方案。

(1)土石方工程采用人工挖土方，放坡系数为1:0.5，待挖土至设计标高进行验槽，验槽合格后进行下道工序。

(2)砌筑工程的墙身用皮数杆控制，先砌外墙后砌内墙，370mm墙采用单面挂线，以保证墙体平整。

(3)屋面防水分项工程的防水材料进场后，检查出厂合格证后即可使用。

(4)扣件式钢管脚手架的作业层非主节点处的横向水平杆的最大间距不应大于纵距的3/4。

[问题]

扣件式钢管脚手架的作业层上非主节点处的横向水平杆，宜根据什么来设置间距？