问题 单项选择题

下列有关折返的描述,不正确的是()

A.心脏两个或多个部位的传导性与不应期各不相同,相互连接形成一个开放环

B.其中一条通道发生单向传导阻滞

C.另一通道传导缓慢,使原先发生阻滞的通道有足够的时间恢复兴奋性

D.原先阻滞的通道再次激动,从而完成一次折返激动

E.冲动在环内反复循环,产生持续而快速的心律失常

答案

参考答案:A

单项选择题
阅读理解

The first bullet "train designed and manufactured in China with a speed of 300 kilometers per hour roiled off the production line on Saturday morning. The train was the latest model in the country' s China Railway High-speed (CRH) Series. This marks that China has joined a leading world club after Japan, France and Germany to become the fourth country capable of turning out such high speed trains. Previously, China' s fastest selfdeveloped trains ran at a service speed of up to 250 km per hour.

Those trains, which presented to public on April 18, served the Beijing-Harbin, Beijing-Shanghai and Beijing-Guangzhou routes. The new streamlined train was made of aluminum alloy(铝合金). The train body was the lightest of its kind in the world; Such a design was for the sake of energy economization. The train' s power was 12.7 kilowatts, lower than other high-speed trains, which was normally about 15 kilowatts.

The new train, which features a bar in the dining car and double-faced LCD TV screens in the first-class cars, was equipped with shock absorbers between carriages. As the train is running at a high speed, the shock absorbers are used to reduce shocking force and rocking of the train body. A train with eight carriages could seat about 600 passengers. They were expected to run on the 115-km Beijing-Tianjin route starting from August before the Beijing Olympic Games. It would reduce the journey time from the current 80 minutes to around 30 minutes.

77. From the 1st paragraph we learn that_______.

A. The latest model of CRH Series ran at a service speed of up to 250 km per hour

B. China became the fourth country in the world able to produce bullet trains

C. The first self-developed bullet train roiled off the production line at a speed of 300 km per hour

D. China has joined a leading world club consisting of Japan ; France and Germany

78. The new bullet train_______.

A. has been put into use in China                    B. has double-faced LCD TV sets in first carriage

C. is slower than high-speed trains                  D. is made of the lightest material in the world

79. "It" in the last paragraph refers to_______.

A. a train with eight carriages                    B. the speed of 115 km per hour

C. the Ministry of Railways                       D. the use of the new train

80. What is mainly talked about in this passage.'?

A. The bullet trains designed and made in China have been put into operation.

B. The bullet trains serve many of the main routes between big cities in China.

C. The new bullet trains are equipped with some advanced facilities.

D. The new bullet trains are expected to run for the Beijing Olympic Games.