4. Which of the following， if presented as the first sentence of a succeeding paragraph， would most logically continue the discussion presented in the passage？
［A］ Ships are another possibility， but they would need to stop every 50 kilometers to lower measuring instruments.
［B］ To understand how ocean acoustic tomography works， it is necessary to know how sound travels in the ocean.
［C］ Timekeeping in medical tomography must be precise because the changes in travel time caused by density fluctuations are slight.
［D］ These variations amount to only about 2 to 3 percent of the average speed of sound in water， which is about 1500 meters per second.
5. The author mentions EL Nino primarily in order to emphasize 。
［A］ the difficulty of measuring the ocean’s largescale currents.
［B］ the variability of mesoscale phenomena.
［C］ the brief duration of weather patterns.
［D］ the possible impact of mesoscale fields on weather conditions.
核心词汇
circulation n. 流通，循环，发行量
identify v.识别;（with）把…和…看成一样，打成一片
dominate v. 支配，占优势
mesoscale n. & a.［气］ 中尺度（的） ，中等规模的
fluctuate v. 变动，上下，动摇 v. 使动摇
velocity n. 速度，速率
phenomenon n. 现象（pl.phenomena）
equatorial a. 近赤道的，赤道的
prohibitive a. 禁止的，抑制的，类同禁止的
conventional a. 普通的，常见的，习惯的，常规的
feasible a. 可行的，可能的
tomography n. 断层摄影术
salinity n. 盐浓度，盐分
density n. 密度
acoustic a. 美声的，听觉的，音感教育，音响学的
难句剖析
1. But in the 1950’s and the 1960’s， researchers began to employ newly developed techniques and equipment， including subsurface floats that move with ocean currents and emit identification signals， and ocean-current meters that record data for months at fixed locations in the ocean.
【解析】 这是一个复合句。 本句的主干结构为researchers began to employ… techniques and equipment…; that move… signals 和that record data… in the ocean 均为定语从句，先行词分别是floats 和meters，floats 和meters 为并列成分。
【译文】 但是到了二十世纪五六十年代，研究者们开始使用新技术和新设备进行研究，其中包括：能够跟随洋流移动并发射出辨识信号的水下漂流仪器和能够在海洋中的一个固定地点持续数月纪录数据的洋流仪表。
2. Mesoscale phenomena may， in fact， play a significant role in oceanic mixing， airsea interactions， and occasional—but far-reaching—climatic events such as El Nino， the atmospheric-oceanic disturbance in the equatorial Pacific that affects global weather patterns.
【解析】 这是一个复合句。 句子结构为Mesoscale phenomena may， in fact， play a significant role in…;in fact 是插入语;interactions和climate events 是并列成分;that affects global weather patterns 是定语从句，修饰disturbance.
【译文】 事实上，紊流现象可能在空气和海洋的互相影响中扮演了重要角色，也在一些偶尔发生但却影响深远的气候现象中扮演重要角色，比如厄尔尼诺就是这样一种在赤道太平洋地区通过大气和海洋的相互干扰来影响全球气候的现象。
3. It is primarily this multiplicative increase in data obtained from the multipath transmission of signals that accounts for oceanographers’ attraction to tomography： it allows the measurement of vast areas with relatively few instruments.
【解析】 这是一个复合句。句子主干为 It is …increase…that accounts for …attraction…; obtained from…signals 为过去分词短语作定语，修饰data;冒号表示解释说明。
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