When we make tea and coffee we use energy: gas, electricity and coal. Global warming comes from energy we use. So each time we make a cup of tea we make a problem for our world. People drink 229 million cups of tea and coffee every day. We should save the energy we use to make tea and coffee. If we want three cups of tea, we should put three cups of water in the kettle. But often we put in five or six cups of water. We use 90 seconds more for a kettle with three cups than for a kettle with one cup. So each time we use a kettle we should save energy. We should think: how many cups do I want? Water is a problem too. How can we save energy, save water and be healthy?
Present Perfect — настоящее совершенное время, которое обозначает действия, уже совершившегося в предшествующий период до момента речи, но имеющего непосредственную связь с настоящим моментом.