Explanation: The major cause of global warming is the increasing concentration of carbon dioxide (CO₂) in the atmosphere. CO₂ is a greenhouse gas that traps heat radiating from the Earth's surface, preventing it from escaping into space — a phenomenon known as the greenhouse effect. Human activities such as the burning of fossil fuels, deforestation, and industrial emissions have significantly increased CO₂ levels, leading to a rise in the Earth’s average temperature, melting of glaciers, rising sea levels, and climate change.

The aorta is the largest artery in the human body. It originates from the left ventricle of the heart and distributes oxygenated blood to all parts of the body through its various branches. The aorta has thick, elastic walls that can withstand the high pressure of blood pumped directly from the heart. It is divided into parts such as the ascending aorta, aortic arch, and descending aorta.

Other options (for context)

• Capillary: The smallest blood vessels where exchange of gases and nutrients occurs.
• Vena cava: The largest vein, not an artery; it carries deoxygenated blood back to the heart.
• Pulmonary vein: Carries oxygenated blood from the lungs to the heart but is not the largest vessel.

Explanation: The speed of light is maximum in a vacuum (approximately 3 × 10⁸ m/s) and decreases as it passes through denser media. Among the given options — vacuum, air, water, and glass — light travels slowest in glass because glass has the highest refractive index (around 1.5). The greater the refractive index, the slower the light travels. This slowing down of light causes refraction, or bending of light, when it passes from one medium to another.

Explanation: A Local Area Network (LAN) is a network of computers and peripherals confined to a small geographical area, such as a home, school, or office building. It enables resource sharing, file transfer, and communication among connected devices within the limited range.

The Ramsar Convention is an international treaty for the conservation and sustainable use of wetlands. Signed in 1971 at Ramsar, Iran, it aims to preserve wetlands as habitats for biodiversity, especially for migratory birds. It promotes wise use of wetland ecosystems through local and national actions.

• Mountain: Conserved under other ecological programs.
• Grassland: Managed under terrestrial biodiversity initiatives.
• Forest: Covered under the UN Forest Forum, not Ramsar.

The O blood group, specifically O negative (O−), is considered the Universal Donor because it can be safely transfused to people of all other blood groups. This is due to the absence of A and B antigens on red blood cells, minimizing the risk of immune reactions during transfusion.

• A: Can donate only to A and AB groups.
• AB: Universal recipient, not donor.
• B: Can donate only to B and AB groups.

Explanation: The colour of the sky without an atmosphere would appear black. On Earth, the sky looks blue because molecules in the atmosphere scatter sunlight — a phenomenon called Rayleigh scattering. Shorter wavelengths of light (blue and violet) are scattered more than longer wavelengths (red). However, if there were no atmosphere to scatter sunlight, no light would be diffused in all directions, and the sky would appear completely dark or black, just as it does from the surface of the Moon or in outer space.