3. What causes seasonal changes in Earth's climate? a. Changes in ocean currents b. Variations in wind patterns c. Changes in atmospheric pressure d. Earth's tilted axis and revolution around the sun 4. How frequently does El Niño typically occur? a. Every 3-8 years b. Annually c. Every 10-15 years d. Every 20 years

3. The correct answer is d. Earth's tilted axis and revolution around the sun.<br /><br />The seasonal changes in Earth's climate are primarily caused by the tilt of Earth's axis and its revolution around the sun. The tilt of Earth's axis causes different parts of the planet to receive varying amounts of sunlight throughout the year. As Earth orbits the sun, the tilt of its axis causes the Northern and Southern Hemispheres to receive different amounts of sunlight, leading to the changing seasons.<br /><br />4. The correct answer is a. Every 3-8 years.<br /><br />El Niño is a climate phenomenon that occurs when the surface waters of the eastern and central tropical Pacific Ocean become unusually warm. El Niño typically occurs every 3-8 years, with an average frequency of about 4-7 years. It can have significant impacts on global weather patterns, including changes in precipitation, temperature, and storm activity.