People walking through the city are not only walking in space, but also crossing time. The completeness of time series is the context and spectrum of a city. "It" is tied to the blood and temperament of a city. Capital and technology can make cities change rapidly. It is tall, but it cannot make the city long. A modern handicraft made of many gold and silver jewellery may not be as valuable as a simple and even slightly damaged Song Dynasty porcelain vase. The value between them is only It's time. "It" in this passage refers to (it). ['Space.', 'Time.', 'The context and spectrum of the city.', 'Complete timing.']