Time travels back to the last years of the Cheng Dynasty, when a minor official from the Ministry of Industry was tied to a river embankment when he opened his eyes - the downstream magistrate wanted to kill him as a sacrifice to the river god. The floodwaters have overflowed the levees and 30,000 people are waiting to drown. The protagonist stared at the raging Yellow River, and a mechanical voice sounded in his mind: [Civilization disease detected: Yellow River flooding. Refining Plan A: Reinforce the river embankment with cement (requires 3,000 tons of limestone)... Plan C: Blow up the upstream mountain to change its course (requires black powder formula)] He raised his head and said to the magistrate who raised his knife: "Give me three days to change the course of the Yellow River." The whole place was dead silent.
