英语精读练习（二）：说明文与议论文专练

Every autumn, millions of birds fly thousands of kilometers south to spend the winter in warmer places. In spring, they return to the exact same nesting spots where they were born. How do they find their way across such great distances without a map or GPS?

Scientists have discovered that birds use several navigation methods at the same time. The most important one is the Earth's magnetic field. Birds have tiny particles of a magnetic mineral called magnetite in their beaks, which work like a built-in compass. Experiments have shown that when scientists place strong magnets near a bird's head, the bird becomes confused and cannot find its way.

Birds also use the sun and stars to navigate. During the day, they track the sun's position across the sky. At night, some species use star patterns to determine which direction is north. Young birds learn these star patterns during their first summer by watching the night sky.

In addition, birds rely on landmarks. They remember mountains, rivers, coastlines, and even highway intersections. Some studies suggest that birds can also smell their way home — pigeons, for example, can recognize the unique smell of their home area from over 100 kilometers away.

What is remarkable is that no single method works alone. If one system fails — say, the sky is cloudy and stars are invisible — birds switch to another system. This combination of tools makes their navigation one of the most reliable systems in nature.

In many countries, it is common for high school students to work part-time after school or on weekends. In China, however, this practice is less common. Some people believe that students should focus entirely on their studies, while others argue that part-time work teaches valuable life skills. Who is right?

Supporters of part-time jobs point out several benefits. First, working helps students develop a sense of responsibility. When you have a boss and customers depending on you, you learn to manage your time and take your duties seriously. Second, it gives students a chance to explore different careers before going to college. A student who works at a bookstore may discover a love for publishing, while one who helps at a community center may decide to study social work.

Third, earning their own money helps students understand its value. Studies show that teenagers who earn their own pocket money tend to be more careful with spending and better at budgeting as adults.

On the other hand, opponents worry that working too many hours will hurt students' academic performance. A 2024 study in the UK found that students who worked more than 15 hours per week scored significantly lower on exams than those who did not work. Sleep and exercise time were also reduced.

The key, most experts agree, is balance. A few hours of work per week can provide benefits without harming studies. But when work becomes a student's main activity, the cost to education is too high. Perhaps the answer is not "should students work?" but "how much is too much?"