【正确答案】As a precious cultural heritage left by ancient people, rock-painting can be said as an encyclopedia recording the early social lives of human, which not only transmits the ancient civilization with long times, but also serves a witness of the culture, religion, folk-custom and ancient artistic history of prehistory people. China is one of the countries whose rock-carvings boast the earliest creation, the widest distribution and the richest content in the world, while Helan Mountain is one of the regions whose rock-carvings boast the most concentrated distribution, the widest theme and the best preserved condition in China. In the depth/hinterland of Helan Mountain, more than 20 relic places with rock-paintings have been discovered, among which, the most representative ones are those at the mouth of Helan Mountain. There are some 6000 rock-paintings near the mouth of Helan Mountain, among which rare rock-paintings of human faces hits over 70. According to research and study, the rock-paintings at the mouth of Helan Mountain were carved during different periods, and most were created by nomad nationality in north China. These rock-paintings are characterized by rough and adorned sculpt, as well as simple and natural composition, of vivid animals such as cattle, horses, donkeys, deer and tigers, as well as human heads carrying thousands expressions. The rock-paintings are faithfully recorded by ancient people of their pursuits and aspirations for happy life in future as well as their personal experiences and feelings based on understanding and thoughts of then social reality, meanwhile leaving these mysterious and magnificent rock-painting heritages in Helan Mountain. Some scholars said that Helan Mountain are created by prehistory people as their sacrifice place by virtue of natural charm, while some held that rock-paintings here are drawing writings before pictographs, through which people take paints to express their ideals, wishes, happiness and sadness before the creation of characters. In this way, “Heaven Book” of prehistory people has been written on the everlasting Helan Mountain.