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【单选题】
In every major city in America, commuters are spending more and more time in their cars fighting traffic. The Texas Transportation Institute recently reported that the average commuter spends an extra 46 hours--more than a full workweek--each year caught in traffic. A major source of the congestion is freight trucks. One large truck takes up the space of almost four cars, and the average truck is becoming longer, with more use of double-and triple-trailers. Increases in truck volume, obviously, add to commuting problems, and according to the U. S. Department of Transportation, freight volume is expected to increase by two-thirds over the next 20 years. One proposed solution--building new roads--is expensive and politically contentious. But there's another way: greater use of freight rail. One freight train can carry the cargo of 500 trucks, and one intermodal train can carry nearly 300 truck trailers. Trucking companies and railroads already are forming intermodal partnerships that combine the best of both kinds of transportation. In an urban area like New York, shifting 25% of freight from trucks to freight trains by the year 2025 would reduce drivers' commuting time by 52.9 hours. In addition, such a shift would save $734 per household in annual congestion costs. Shifting freight from road to rail also helps the environment. Freight rail is more fuel-efficient per ton-mile than trucks. And it reduces drivers' fuel consumption by decreasing the time they spend idling in traffic. By 2025, commuters in New York could save 254 gallons of fuel with a 25% shift of freight from truck to rail. Air pollution levels also would improve with an increase in the use of freight rail. For instance, that same 25% shift to rail by 2025 would decrease air pollutants New York by as much as 79,500 tons. To carry out these changes, the freight rail industry will need more capacity, but that depends on return on investments. Because railroads are not meeting their cost of capital, government policymakers may want to consider investment incentives to help meet the growing demand for freight rail. This would enable freight railroads to provide convenient, on-time, quality service to shippers and boost their share of freight transport. It is hard to imagine a less costly or more effective strategy for reducing traffic congestion. In the last 2nd paragraph, the basic problem with the freight rail industry is that ______ .
A.
it only has a very low capacity
B.
the price of its service is too low
C.
its services are not very convenient
D.
it is not a profitable enough business
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参考答案:
举一反三
【单选题】存储状态位和控制位的特殊功能寄存器是( )。
A.
PC
B.
SR
C.
IE
D.
SP
【简答题】单片机复位后,特殊功能寄存器SP的初始状态是(    )。
【判断题】挤压系统中,光滑的螺杆和粗糙的料筒内壁,有利于物料的输送。
A.
正确
B.
错误
【单选题】MCS—51 的专用寄存器 SFR 中的堆栈指针 SP 是一个特殊的存贮区,用来 ( ),它是按后进先出的原则存取数
A.
存放运算中间结果
B.
存放标志位
C.
暂存数据和地址
D.
存放待调试的程序
【单选题】机构处于死点位置时其压力角为( )。
A.
B.
45º
C.
60º
D.
90º
【单选题】对含有n个元素的顺序表采用直接插入排序方法进行排序,在最好情况下算法的时间复杂度为 。
A.
O(n)
B.
O(nlog2n)
C.
O(n2)
D.
O()
【单选题】SP是 位特殊寄存器。
A.
4位
B.
8位
C.
16位
D.
32位
【单选题】存储状态位和控制位的特殊功能寄存器是 ( ) 。
A.
PC
B.
SR
C.
SP
【单选题】对含有 n 个元素的顺序表采用直接插入排序方法进行排序,在最好情况下算法的时间复杂度为( )
A.
O( n )
B.
O( n log 2 n )
C.
O( n 2 )
【简答题】单片机复位后,特殊功能寄存器SP的初始状态是(    )H。
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