题目内容：

Bike sharing have become popular words in cities from Cape Town to Shanghai to Melbourne. Planners, politicians and media keep showing off their benefits: reducing pollution, congestion, travel costs and oil dependence, while improving public health. Bike sharing also helps make cities appear modern, dynamic and world-wide—qualities much sought after by the creative class.

But what makes for a successful public bike-sharing program? This is an important question because installing one requires significant public and private investment and adjustment to the built environment.

While many programs have been launched among much praise, often their popularity has soon declined. Many end up operating at a financial loss and depend on other profitable enterprises to cross-subsidize(交叉补贴) them. Some have resulted in thrown-away bikes becoming an eyesore.

Understanding which factors enhance or stop public bike sharing is critical in helping cities decide whether such a program is workable, before considering what design and sitting will work best.

Drawing on current knowledge, we discuss the importance of the local landscape, climate, cycling infrastructure (基础设施) and land use. We also touch on other factors, such as the legal environment and the characteristics of the bike-sharing program itself.

Take natural environment for example. Two natural environment factors are known to affect participation: hilliness and weather. Hilliness discourages balanced bike-sharing use, as users avoid returning bicycles to stations on hilltops. Those stations end up being empty, while stations on flat areas are often full, so users cannot find a station to return their bikes.

As for weather, ideal temperature ranges vary by the climate zone. Case studies show warm and dry weather encourages public bike-sharing use. Rain and strong wind reduce the frequency of trips. However, some approaches, such as providing sheltered, shaded, or even heated or cooled cycling infrastructure, could prove useful.

1.What can we infer about bike sharing from Paragraph 1?

A. It has no disadvantage.    B. It is welcomed worldwide.

C. It can solve every problem.    D. It is the symbol of modern cities.

2.What is the current situation of bike-sharing programs?

A. Many of them run at a loss.    B. Most of them make huge profits.

C. They are the most promising business.    D. Their development is determined by public investment.

3.Why does the author mention the natural environment?

A. To show user’s interest in various natural environment.

B. To show the decisive function of natural environment.

C. To show the necessity of bike-sharing programs.

D. To show the significance of some factors.

4.Which of the following might increase bike-sharing use?

A. Hilliness.    B. Attractive bikes.

C. Rain and strong wind.    D. Perfect cycling infrastructure.