1. Forms of Locomotion

2. Thermal Stratification

3. Attempts at Determining Earth's Age

4. Constraints on Natural Selection

5. Cosmological Principle

Thermal Stratification第4题，当时300+的学生群里，只有3位同学作做对，且同学们针对这道题讨论了一整天。昨天能作对这题且知道为什么的同学，阅读基本上26分的水平有了。如果做错也别担心，因为这道题真的很难很难，我们还是通过每周的群内讲座才解释清楚的。所以，说不定咱只错了这道题错呢？

原题：

This rapid absorption of sunlight by water has two important consequences. First, it means that photosynthesisthe process by which plants use the energy of sunlight to produce the organic carbon compounds necessary for lifecan only occur in surface waters where the light intensity is sufficiently high. Species that produce their own organic carbon compounds are called primary producers, and they are the base of the marine food web. Virtually all of the photosynthesis that supports the rich life of oceans and lakes comes from plants living in the upper 10 to 30 meters of water. Along shores and in very shallow bodies of water, some species such as kelp are rooted to the bottom. These plants may attain considerable size and structural complexity, and may support diverse communities of organisms. In the open waters that cover much of the globe, however, the primary producers of organic carbon are tiny, often one-celled algae (called phytoplankton), which are suspended in the water. Zooplankton, tiny invertebrates that feed on phytoplankton, migrate vertically on a daily cycle: up into the surface waters at night to feed and down into the dark, deeper waters during the day to escape predatory fish that rely on light to detect prey.

4.According to paragraph 3, all of the following are true of kelp EXCEPT:

A. They are found at the bottom of shallow waters.

B. They are the primary producers of organic carbon.

C. They can grow very large.

D. They are a source of food for a variety of organisms.

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答案是A。

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