The ureter is a tube that connects each kidney to the urinary bladder. Its primary function is to transport urine produced in the kidneys to the bladder for storage before excretion. Each person has two ureters, one from each kidney. Urine moves through the ureters by peristaltic movements, which are wave-like contractions of the muscular walls. The urethra is a different structure that carries urine from the bladder to the outside of the body. The nephron is the functional unit of the kidney responsible for filtering blood. Urination is a process, not a structure. Thus, ureter is the correct answer. Understanding the urinary system is important for studying human physiology and maintaining health awareness.

Ethiopia experienced a severe famine during 1983–1985, which became one of the most well-known humanitarian crises of the 20th century. It was caused by a combination of drought, political instability, and poor agricultural policies. The famine led to widespread starvation and the deaths of hundreds of thousands of people. It also triggered global humanitarian efforts, including aid campaigns and awareness programs. This event highlighted the importance of food security, disaster management, and international cooperation in addressing crises. Other periods listed are incorrect for this major famine. Thus, 1983–1985 is the correct answer, representing a significant historical event in global humanitarian efforts.

Producers, mainly green plants, require nitrogen for synthesizing proteins, nucleic acids, and chlorophyll. However, they cannot directly use atmospheric nitrogen (N₂), which is chemically inert. Instead, they absorb nitrogen in usable forms such as ammonia (NH₃), ammonium ions (NH₄⁺), or nitrates (NO₃⁻). Ammonia is produced through biological nitrogen fixation by certain bacteria, which convert atmospheric nitrogen into a form plants can absorb. This process is crucial for maintaining the nitrogen cycle in ecosystems. CO₂ is used by plants in photosynthesis but does not provide nitrogen. N₂, although abundant in the atmosphere, cannot be directly utilized by plants without conversion. NH₄NO₃ is a fertilizer that provides nitrogen, but the fundamental absorbed form at the biochemical level is ammonia/ammonium. Thus, NH₃ is the correct answer. Understanding nutrient cycles is essential for grasping ecosystem functioning and is a common topic in competitive exams. This concept highlights the importance of microorganisms in supporting plant life and maintaining ecological balance.

Sunspots are dark regions that appear on the surface of the Sun due to intense magnetic activity that lowers the surface temperature in those areas. The first recorded telescopic observation of sunspots is credited to Thomas Harriot, an English astronomer, in 1610. He used an early telescope to observe the Sun and documented these spots before Galileo’s more widely known observations. This discovery challenged the long-standing Aristotelian belief that celestial bodies were perfect and unchanging. The presence of spots on the Sun suggested that it was dynamic and imperfect. Later astronomers such as Galileo Galilei and Christoph Scheiner studied sunspots more extensively and tracked their movement, which helped establish that the Sun rotates on its axis. Albert Einstein is known for the theory of relativity, Isaac Newton for gravity and laws of motion, and René Descartes for contributions to philosophy and mathematics. None of them observed sunspots first. Thus, Thomas Harriot is considered the earliest observer, making option D correct. His work contributed significantly to the development of modern astronomy and our understanding of solar activity.

The human brain is composed of approximately 75% water, making it one of the most water-rich organs in the body. Water is essential for maintaining brain function, including nutrient transport, temperature regulation, and electrical activity. Adequate hydration is crucial for cognitive functions such as memory, concentration, and alertness. Even mild dehydration can impair brain performance. The other percentages are either too low or too high to accurately represent the brain’s composition. Thus, 75% is the correct answer. This emphasizes the importance of water in maintaining overall health and brain function.