Practice Test 20: Tidal Power and Children's Language Learning

A Every day, the gravitational pull of the Moon and, to a lesser extent, the Sun raises and lowers the level of the oceans. This rhythm of tides is among the most predictable events in nature: engineers can forecast the height of the water at a given harbour years in advance. Wind and sunshine vary with the weather, but tides do not, and this reliability is what attracts those who look for renewable sources of electricity.

B The oldest approach is the tidal barrage, a dam built across an estuary. As the tide comes in, water flows through turbines in the dam, and it flows through them again as the tide goes out. The best known example is on the Rance estuary in France, which opened in 1966 and has generated electricity for more than half a century. Yet very few barrages have followed it. They are expensive to build, and by changing the flow of water in an estuary they can damage the mud flats on which wading birds and other wildlife depend.

C A newer approach avoids the dam. Tidal stream turbines resemble underwater windmills and are anchored to the sea bed in places where currents are strong, such as narrow channels between islands. Because they block only a small part of the flow, they disturb the surroundings far less than a barrage. The technology is still maturing, however, and turbines must withstand salt water, powerful currents and the difficulty of maintenance beneath the waves.

D Supporters of tidal power argue that its value lies less in the amount of electricity it produces than in the way it complements other sources. A grid with a large share of wind power needs something to fill the gaps when the air is still. Since the tides follow a timetable that is entirely independent of the weather, tidal plants can supply power at times when wind and solar plants cannot. Whether this advantage will outweigh the high cost is the question that investors are still debating.

A It is a common belief that children learn languages more easily than adults. Parents who move abroad often watch their young children chatter confidently in a new language within months, while they themselves still struggle with basic phrases. The belief is not entirely wrong, but research shows that the picture is more complicated than the saying suggests.

B One explanation is the so called critical period, the idea that the brain is especially receptive to language early in life and becomes less so after puberty. The strongest evidence concerns pronunciation: people who begin a second language in early childhood are far more likely to speak without a foreign accent than those who begin as adults. Yet scientists disagree about whether the change is sudden or gradual, and many prefer to speak of a sensitive period rather than a fixed deadline.

C In other respects, adults have advantages. In controlled studies over a few months, older learners often make faster progress in vocabulary and grammar, because they can use study strategies and knowledge of how their first language works. Children's apparent speed owes much to the amount of time they spend in the language. A child in an immersive school hears the new language for hours every day and is rarely embarrassed about making mistakes.

D The practical lesson is therefore encouraging for adults. Although most will not sound like native speakers, many can reach a high level of fluency if they can create the conditions that children enjoy: plenty of exposure, regular conversation and tolerance of error. Researchers add that motivation matters greatly. An adult who needs the language for a job or a family is likely to make steadier progress than one who studies it casually.