Đề ôn thi Đề thi vào lớp 10 Trường THPT Chuyên KHXH môn Tiếng Anh - Mã đề KHXH-72

The Sun, at the center of our solar system, provides the heat and light essential for life on Earth. But what is this massive ball of fire made of? It isn't solid or liquid, but an incredibly hot ball of gas. The Sun is (35) __________ giant star, and like others, its composition is simple yet fascinating. Understanding its components helps us comprehend the processes that power our solar system.

Scientists have studied the Sun's light to learn its ingredients. It is mainly (36) __________ of two primary gases: hydrogen and helium. Approximately 74% of the Sun’s mass is hydrogen, and about 24% is helium. These two elements together make up 98% of the Sun. The small remaining percentage consists of a mix of heavier elements like oxygen and carbon.

This transformation happens deep inside the Sun’s core. Here, the temperature and pressure are immense; (37) __________, hydrogen atoms are squeezed so forcefully that they fuse into helium. This process, nuclear fusion, (38) __________ an enormous amount of energy as light and heat, which then travels through space to our planet.

Early astronomers explained that the Sun (39) __________ trace amounts of other elements too. This discovery was crucial for (40) __________ the life cycle of stars. However, compared to the vast amounts of hydrogen and helium, these heavier elements are just a (41) __________ in the ocean, representing less than 2% of its mass.

The conditions in the Sun's core are essential. If the Sun’s core were not so hot and dense, this fusion reaction (42) __________. The balance between gravity pulling inward and the energy from fusion pushing outward is what keeps our Sun stable, allowing it to shine for billions of years.

Before you could stream movies instantly or join online classes without interruption, the internet was a very different place. For many families in the 1990s and early 2000s, connecting to the web meant using a dial-up modem. This connection was incredibly slow, making a strange series of beeps and squeals as it established a link over a telephone line. Downloading a single song could take over ten minutes, and the internet connection would be lost if someone picked up the phone. It was a primitive but revolutionary technology for its time, opening the first door to the digital world.

The first major improvement was the arrival of ADSL (Asymmetric Digital Subscriber Line). This 'broadband' technology was a significant leap forward. It was 'always on,' meaning you didn't have to dial in each time, and it was much faster than dial-up. Crucially, it used the same copper telephone wires that were already installed in most homes, making the upgrade relatively straightforward for telecommunication companies. However, the speed of ADSL was limited by the physical properties of copper and the distance from the user's home to the telephone exchange.

The true revolution in internet speed came with fiber optic technology. Instead of sending electrical signals through copper wires, fiber optic cables transmit data using pulses of light that travel through extremely thin strands of glass. They can carry massive amounts of information at nearly the speed of light, making them far superior to copper cables in both speed and reliability. This technology is less affected by distance or electrical interference, providing a stable and consistent connection capable of handling high-definition video streaming, competitive online gaming, and large file downloads simultaneously.

In Vietnam, this technological shift has been dramatic and rapid. Companies like the state-owned VNPT and private corporations such as FPT Telecom have invested heavily in replacing the old copper infrastructure with a vast network of fiber optic cables. This massive undertaking has brought high-speed internet not just to major cities like Hanoi and Ho Chi Minh City, but also to more rural and remote areas. This national effort in digital transformation ensures that more and more people can access the opportunities of the modern digital economy.

For teenagers today, this powerful infrastructure is the invisible foundation of daily life. It's the reason you can collaborate on a school project over a video call, watch your favorite YouTubers without buffering, or compete in online games with players from around the world. The journey from the screech of a dial-up modem to the silent, lightning-fast pulse of a fiber optic cable is a remarkable story of engineering that makes your digital life possible.