Giving examples - Freshwater ecosystems - rivers and lakes. / Marine ecosystems - such as the sea / Some human activities - agriculture ... , Describing a process - First, food is chewed in the mouth... Then this food moves down the... Next it mixes with gastric juices... Finally, it leaves the stomach and ..., Expressing conditions - If there are lots of vibrations, the frequency is high. / If there are few vibrations, the sound has a low pitch., Describing trends in the present - The population is ageing. The birth rate is decreasing. People are living longer., Talking about purpose - Fish use their fins to swim. Turtles have a shell to protect their body. Dolphins surface to breathe., Defining - Nutrients are substances which our body needs to survive. Diet is the food wich someone normally eats. Blood vessels are tubes which transport blood.,

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