The correct answer is option 1, the Andes mountains. The Andes mountains are the longest mountain chain on Earth, stretching about 7,000 kilometers (4,300 miles) along the western coast of South America. They span through several countries including Argentina, Bolivia, Chile, Colombia, Ecuador, and Peru. The Andes are characterized by towering peaks, deep valleys, and active volcanoes. They are a result of tectonic plate movements and are known for their geological and ecological diversity. Option 2, the Mid-Atlantic ridge, is an underwater mountain chain that runs down the center of the Atlantic Ocean, but it is not the longest. Option 3, the Western Cordillera, refers to the mountain ranges along the western edge of North and Central America, but it is not the longest either. Option 4, the Himalayan range, is the highest mountain range on Earth, but it is not the longest.