The world’s largest mountain ranges, known as the “Young Fold Mountains” (like the Himalayas, Alps and Andes), were formed approximately 30 million years ago during the Tertiary period. This “Alpine Orogeny” was driven by intense plate tectonic collisions. These mountains are characterized by their great height, steep slopes and ongoing tectonic activity, as they are geologically “young.” ANSWER: (B) 30