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1. We studied earthquakes at school.

2. The tsunami in Thailand was a terrible accident for thousands of people.

3. Tornados happen very often in the USA.

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1. Where do hurricanes always begin?

2. Which city has the most rain and floods?

3. How fast can a tsunami travel?

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1. Holidaymakers should not litter in the forests.

2. Sometimes people don't survive in the earthquake.

3. The pollution of the environment was not discussed during the last UN summit.

утвердительные и положительные предложения - это одно и то же:-))