Hi Bethesda, On second thoughts I am not happy with my reasoning for answer 7. What about Taiga as the answer? It is mentioned on page 852 (haven`t had a chance to look elsewhere yet). Taiga is a vast area.
Thanks for pointing out that 17,226,000 was on page 596. As you know this is the area of Asia in square miles. If you add the areas of Antarctica, Europe, and Australia in square kilometres you will see this totals 31,601,501. This number of square kilometres will easily fit into 17,226,000 square miles. I hope this is helpful.