5 When the author found The BurgerShack had no waiters, he________.

A. was quite angry B. volunteered to get the food

C. decided to locate a table D. was very curious

6.What do we know about the BurgerShack?

A. It was very famous for its style B. It was a self-service restaurant

C. It had a quiet environment inside D. It was crowded with dining tables

C

　Many traffic jams leave drivers puzzled as they finally reach the end of a tail-back to find no visible cause for their delay. Now, a team of mathematicians have found the answer by developing a model to show how major delays occur on our roads, with no apparent (显然的) cause.

The model showed that a driver, slowing down below a critical speed (极限速率) when reacting to unexpected events, forces the car behind to slow down further and the next car back to reduce its speed still further. The result of this is that several miles back, cars would finally come to a stop, with drivers unaware of the reason for their delay. The model predicts that this is a very typical situation on a busy highway (above 15 vehicles per km). The jam moves backwards through the traffic creating a so-called "backward travelling wave", which drivers may encounter many miles upstream, several minutes after it was caused.

Drivers and policy-makers have not previously known why jams like this occur, though many have put it down to the sheer volume of traffic. While this clearly plays a part in this new theory, the main issue is around the smoothness of traffic flow. According to the model, heavy traffic will not automatically lead to jams but can be smooth-flowing. This model takes into account the time delay in drivers' reactions, which lead to drivers braking more heavily than if they had identified (识别) and reacted to a problem ahead a second earlier.

When a driver taps the brake, the traffic may come to a full standstill several miles behind. It really matters how hard a driver brake - a slight braking from a driver who has identified a problem early will allow the traffic flow to remain smooth. Heavier braking, usually caused by a driver reacting late to a problem, can affect traffic flow for many miles.

7. From the passage, we learn that __________.

A. drivers are often unaware of the reason why a traffic jam happens

B. many drivers don't know how to deal with unexpected events

C. heavy traffic often forces drivers to slow down

D. traffic jams often happen on a busy highway

8. Which of the following is NOT included in the new theory?

A. Width of roads. B. Traffic speed.

C. Traffic smoothness. D. Delay time.