Beyond the Great Wall and the chain of rugged hills through which it snakes, workers are putting the finishing touches to a colossal edifice. The beams of its roof are curved. The China Pavilion, as the structure is called, is for an international flower festival in Yanqing, a satellite town of the capital. The show will open on April 29th and last for more than five months. It will be the biggest expo of any kind that China has staged under the aegis of the Paris-based Bureau International des Expositions since the Shanghai World Expo in 2010...