A. 2,500 kilometers long The Great Wall of China is.
B. The Great Wall of China is 2,500 kilometers long.
Feedback There is a certain word order in statements: Subject - Auxiliary - Object. 'The Great Wall of China' is a subject, 'is' - an auxiliary verb, '2,500 kilometers long' - an object.
C. Is The Great Wall of China 2,500 kilometers long.
D. The Great Wall of China 2,500 kilometers is long.