单项选择题

What did Steve originally plan to do

A．To go to a park near the beach.
B．To stay at home.
C．To see a new film.
D．To do some study.

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问答题

RED TIDESDifferent events can change the balance of sea life. Red tides are an example. These can happen in oceans, rivers or lakes, anywhere in the world. What happens is that algae suddenly increase in numbers. Algae are single-celled organisms. They are a normal part of sea life. As they spread, or bloom, the water may turn red or brown. Sometimes the water does not change color at all. But deadly algae could still be present. Some kinds of algae produce a strong poison. This can build up in shellfish that eat the algae and make them poisonous, but not kill them. Other kinds of algae may kill sea life by reducing oxygen levels in the water. In some red tides, thousands of dead fish appear on beaches. Scientists do not know exactly why red tides happen. But they say a combination of conditions all play a part. These include water temperature, nutrients in the water and water flow. Pollution could also play a part.

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