tpo25 reading1

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From a plant's evolutionary viewpoint, however, it was also a land of opportunity, free of competitors and predators and full of carbon dioxide and sunlight (the raw materials for photosynthesis, which are present in far higher concentrations in air than in water). So once natural selection had shaped the adaptations that helped plants overcome the obstacles to terrestrial living, plants prospered and diversified.

A. It was exposed to high levels of solar radiation.

D. It lacked the presence of any organisms.

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问题

The environmental conditions of freshwater habitats, unlike those of ocean habitats, are highly variable. Water temperature can fluctuate seasonally or even daily, and changing levels of rainfall can lead to fluctuations in the concentration of chemicals in the water or even to periods in which the aquatic habitat dries up.

具体的

 Ancient freshwater green algae must have evolved features that enabled them to withstand extremes of temperature and periods of dryness. Scientists believe that chemical changes and a thicker exterior, among other things, may have helped ancient algae overcome the conditions in their environment. These adaptations served their descendants well as they invaded land.

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