问题 单项选择题

在某工程网络计划中,工作M的最早开始时间和最迟开始时间分别为第12天和第15天,其持续时间为5天。工作M有3项紧后工作,它们的最早开始时间分别为第21天、第24天和第28天,则工作M的自由时差为()天。

A.1

B.3

C.4

D.8

答案

参考答案:C

解析:

因为M的最早开始时间+持续时间=最早完成时间=12+5=17天。自由时差=各紧后工作的最早开始时间的最小值一本身工作的最早完成时间=min{21,24,28}-17=4天。因此,本题正确答案为C。

阅读理解

A device that stops drivers from falling asleep at the wheel is about to undergo testing at Department of Transport laboratories and could go on sale within 12 months.

The system, called Driver Alert, aims to reduce deadly road accidents by 20% - 40% that are caused by tiredness. Airline pilots can also use it to reduce the 30% of all pilot-error accidents that are related to fatigue.

Driver Alert is based on a computerized wristband. The device, worn by drivers or pilots, gives out a sound about every four minutes during a car journey. After each sound the driver must respond by squeezing the steering wheel. A sensor in the wristband detects this pressing action and measures the time between the sound the driver’s response.

Tiredness is directly related to a driver’s response time. Usually, a watchful driver would take about 400 milliseconds to respond, but once that falls to more than 500 milliseconds, it suggests that the driver is getting sleepy.

In such cases the device gives out more regular and louder sounds, showing that the driver should open a window or stop for a rest. If the driver’s response continues to slow down, the sounds become more frequent until a nonstop alarm warns that the driver must stop as soon as possible.

The device has been delivered to the department’s laboratories for testing. If these tests, scheduled for six months’ time, are successful, the makers will bring the product to market within about a year.

小题1:According to the text, Driver Alert ______.

A.aims to reduce tiredness-related accidents

B.has gone through testing at laboratories

C.aims to prevent drivers from sleeping

D.has been on sale for 12 months小题2:How should a driver respond to the sounds from Driver Alert?

A.By sounding a warning.

B.By touching the wristband.

C.By checking the driving time.

D.By pressing the steering wheel.小题3:We can learn form the text that the driver needs to stop for a break when his response time is ______.

A.about 400 milliseconds

B.below 500 milliseconds

C.over 500 milliseconds

D.about 4 minutes小题4:When the driver gets sleepy while driving, Driver Alert ______.

A.moves more regularly

B.stops working properly

C.opens the window for the driver

D.sounds more frequently and loudly

单项选择题