1. The problem asks which invention allowed Chinese sailors to travel to far-off lands without getting lost. 2. To solve this, we consider the function of each invention: - The magnetic compass helps with navigation by showing direction. - Block printing is for printing texts. - Watertight ship sections help prevent sinking. - Movable type is for printing. 3. Since navigation is about direction and not printing or ship safety, the magnetic compass is the invention that allowed sailors to travel without getting lost. Final answer: The magnetic compass.