II．完形填空。从A、B、C、D四个选项中，选择一个正确答案，并填在答题纸相应的位置上。错选、多选或未选均无分。（本大题共15小题，每小题1分，共15分）

Bridge is a structure used by people and vehicles to cross areas that are obstacles to travel. Without bridges, people would need   16   to cross waterways and would have to travel around such obstacles   17   canyons and valleys.

Bridges range   18   from a few feet or meters to several miles or kilometers. A bridge must be strong enough to support its own weight   19   the weight of the people and vehicles that use it. It must also   20   natural occurrences, including earthquakes, strong winds, and changes in temperature.

Most bridges are held up by at least two supports set in the ground. The   21   between two adjacent supports is called a span of a bridge. The supports at each   22   of the bridge are called abutments (桥墩), and the supports that   23   between the two abutments are called piers. Most short bridges are supported only by abutments and are known as   24   -span bridges. Bridges that have one or more piers   25   the abutments are called multi-span bridges. Most long bridges are multi-span bridges. The main span is the longest span of a multi-span bridge.

Suspension bridges (吊桥) are perhaps the most   26   type of bridge because of their long main span and especially attractive   27   . These bridges have a roadway that hangs from steel cables that are supported by two high towers. Suspension bridges are used to   28   great distances. They are also used to cross deep water or steep canyons, and in other places   29   the construction of piers is especially difficult and   30   . These bridges require only two piers, each of which supports a tower.

16. A. buses                 B. planes                    C. trains                       D. boats

17. A. like                     B. as                         C. with                        D. to

18. A. in height             B. in depth                 C. in length                   D. in width

19. A. as well as            B. by means of           C. except for                D. according to

20. A. prevent               B. resist                     C. beat                         D. fight

21. A. space                 B. extent                     C. distance                   D. stretch

22. A. end                    B. side                       C. way                         D. part

23. A. run                     B. remain                   C. stay                         D. stand

24. A. sole                    B. unique                   C. single                       D. simple

25. A. in proportion to   B. in addition to           C. in place of                D. in front of

26. A. impressive          B. expressive              C. productive                D. constructive

27. A. existence            B. appearance             C. quality                     D. ability

28. A. measure              B. move                     C. extend                     D. span

29. A. while                  B. when                     C. where                      D. which

30. A. profitable            B. practical                C. necessary                 D. expensive