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  3. Water is the oldest form of transportation. The original sailing vessels were replaced by steamboats in the early 1800s and by d

Water is the oldest form of transportation. The original sailing vessels were replaced by steamboats in the early 1800s and by d

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问题     Water is the oldest form of transportation. The original sailing vessels were replaced by steamboats in the early 1800s and by diesel power in the 1920s. A distinction is generally made between deep-water and navigable inland water transport. Domestic commerce centers on the Great Lakes, canals, and navigable rivers.
    In 1975 water transport accounted for 22.6 percent of total intercity tonnage. Its relative share of intercity tonnage was 33.3 percent in 1947 and 31.7 percent in 1958. Tonnage declined to 27.9 per cent in 1965 but increased by 1970 to 28.4 percent. This short-time increase did not stabilize. Market share dropped by 5.8 per cent by 1975. Forecasted market share by 1985 is 18.4 percent of total intercity tonnage. The water transport share of revenue has been less than 2 percent of intercity freight revenue since 1955.
    The exact miles of improved waterways in operation depend in part on whether coastwise and intercostals shipping is included. Approximately 26,000 miles of improved inland waterways were operated in 1975. Fewer miles of improved inland waterways exist than of any other transportation mode.
    The main advantage of water transport is the capacity to move extremely large shipments. Deepwater vessels are restricted in operation, but diesel towed barges have a fair degree of flexibility. In comparison to rail and highway, water transport ranks in the middle with respect to fixed cost. The fixed cost of operation is greater than that of motor carders but less than that of railroads. The main disadvantage of water is the limited degree of flexibility and the low speeds of transport. Unless the source and destination of the movement are adjacent to a waterway, supplemental haul by rail or truck is required. The capability of water to transport large tonnage at low variable cost places this mode of transport in demand when low freight rates are desired and speed of transit is a secondary consideration.
    Freight transported by inland water leans heavily to mining and basic bulk commodities, such as chemicals, cement, and selected agricultural products. In addition to the restrictions of navigable waterways, terminal facilities for bulk and dry cargo storage and loaded-unload devices limit the flexibility of water transport. Labor restrictions on loading and unloading at deck level create operational problems and tend to reduce the potential range of available traffic. Finally, a highly competitive situation has developed between railroads and inland water carriers in areas where paralleled routings exist.
    Inland and Great Lakes water transport will continue to be a fable alternative for future logistical system design. The full potential of the St. Lawrence Seaway has not yet been realized with respect to domestic freight. The slow passage of inland river transport can provide a form of water housing in transit if fully integrated into overall system design. Improvements in icebreaking equipment appear on the verge of emanating the seasonal limitations of water transport.
According to the passage, diesel-towed barges differ from deep-water vessels in that they ______.
选项 A、are less restricted in operation
B、are less flexible
C、are larger shipments
D、are most flexible
答案A
解析 做这道题时要注意几个选项之间的细微差别。根据文章第4段第2句：Deep-water vessels are restricted in operation, but diesel towed barges have a fair degree of flexibility．可知，深水轮自由度小。故正确答案为A。
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