众所周知，非限制性定语从句对先行词起到了补充说明的作用，省略其句意仍然是完整的。正是如此，很多学生在处理阅读中含有非限制性定语从句的长难句时，往往对其视而不见，直奔主干，但一切当然都不是。在托福问题中，有些问题只是非限制性定语从句。下面由新航道的沈阳托福培训小编为您解答！

　　非限制性定语从句在托福阅读中重要吗？

　　The principal seagoing ship used throughout the Middle Ages was the galley, a long, low ship fitted with sails but driven primarily by oars. The largest galleys had as many as 50 oarsmen. Since they had relatively shallow hulls, they were unstable when driven by sail or when on rough water; hence they were unsuitable for the voyage to the East. Even if they hugged the African coastline, they had little chance of surviving a crossing of the Indian Ocean. Shortly after 1400, shipbuilders began developing a new type of vessel properly designed to operate in rough, open water: the caravel. It had a wider and deeper hull than the galley and hence could carry more cargo; increased stability made it possible to add multiple masts and sails. In the largest caravels, two main masts held large square sails that provided the bulk of the thrust driving the ship forward, while a smaller forward mast held a triangular-shaped sail, called a lateen sail, which could be moved into a variety of positions to maneuver the ship.

　　According to paragraph 3, what did the lateen sail contribute to the caravel as a sailing ship?

　　?A.It provided stability for the front part of the ship.

　　?B.It made it possible for the hull to be wider and deeper.

　　?C.It added considerably to the speed of the wind-driven ship.

　　?D.It improved the capacity of the ship to be guided.

　　显然，这是一个事实信息问题，问laten sail对caravel的功能是什么，可以直接定位到最后一句，可见lateen sail是一种三角帆，但它被描述为最终的非限制性定语从句。可以看出，它可以移动到不同的位置来控制帆船，并对应于D选项。因此，这句话中的非限制性定语从句是答题的关键。

　　接下来我们再来看一道简化语句:

　　The explanation is that the Maya excavated depressions, or modified natural depressions, and then plugged up leaks in the karst by plastering the bottoms of the depressions in order to create reservoirs, which collected rain from large plastered catchment basins and stored it for use in the dry season.

　　Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

　　?A.Southern Maya populations obtained the water they needed for the dry season by collecting and storing rainwater in sealed depressions.

　　?B.The Maya are credited with creating methods for modifying natural rainwater and storing it.

　　?C.Leaks in the karst caused difficulties in the creation of reservoirs, which were needed to store water for the dry season.

　　?D.Southern Mayans were more successful at collecting rain than storing it during dry seasons.

　　原话essential information是玛雅人做的三个动作，即excavated depression、modified natural depressions 和plugged up...为createteeateatea reservoirs，然后是非限制性定语从句对reservoir的补充说明，即reservoir的功效，即收集雨水进行补充说明

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