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1·Low average population densities are characteristics of most underdeveloped countries.

平均人口密度低是大多数不发达国家的特点。

2·As densities increased, domestic architecture became larger, culminating in crowded pueblos.

随着密度的增加，住宅建筑变得更大，最终形成拥挤的村庄。

3·The cultivation of crops has expanded into progressively drier regions as population densities have grown.

随着人口密度的增长，农作物的种植已经扩展到了越来越干旱的地区。

4·Rock lobsters prey on sea urchins, and increased rock lobster densities coincided with significant decreases in urchins.

岩石龙虾以海胆为食，而岩石龙虾密度的增加正好与海胆数量的显著减少相吻合。

5·After several generations of population growth, people packed the landscape in densities so high that communal pueblos may have been a necessary outcome.

经过几代人的人口增长，人们以如此高的密度挤满了这个地区，以至于公共聚居地的出现可能是一个必要的结果。

6·By compiling a map of seismic velocities from thousands of earthquakes across the globe, they can also begin to map temperatures and densities throughout the mantle.

通过编制全球数千次地震的地震速度图，他们还可以开始绘制地幔的温度和密度图。

7·The densities of the terrestrial planets average about 5 times the density of water, whereas the Jovian planets have densities that average only 1.5 times the density of water.

类地行星的密度的平均值大约是水的密度的五倍，而类木行星的密度平均值只有水的密度的1.5倍。

8·Crown of thorns starfish normally live in high population densities.

刺冠海星通常生活在聚居的环境中。

9·However, near hydrothermal vents, areas of the ocean where warm water emerges from subterranean sources, live remarkable densities of huge clams, blind crabs, and fish.

然而，在海底热液喷口附近，也就是温暖海水从地下涌出的地方，生活着大蛤、盲蟹和鱼类，数量非常庞大。

10·If the two media have really different densities, like air and water, then most of the energy is going to be reflected back, very little of it will keep going and get transmitted into the new medium.

而如果这两种介质的密度相差较大，就像空气和水那样，那么大部分的能量将会折射回来，只有一小部分会继续传播进入到新的介质中。

(1)high density高密度，密度高

(1)current density电流密度；扩散（弥漫）流密度

(1)low density低密度

(1)power density功率密度；谱线密度；力密度

(1)energy density能量密度

(1)population density人口密度；种群密度