The principle that water and oil do not mix is the basis for the printing method of (A) offset (B) rotogravure (C) photogravure (D) letter-press Correct Ans: (A) Explanation: The principle that water and oil do not mix serves as the foundation for the offset printing method. This widely-used technique relies on the natural immiscibility of water and oil to transfer images precisely onto a printing surface. Offset printing operates by coating the image areas of a printing plate with an oil-based ink while keeping the non-image areas dampened with water. Because oil and water repel each other, the ink adheres only to the image areas and avoids the non-image sections. The plate then transfers the image onto a rubber blanket, which subsequently prints it onto the final surface, such as paper. This method offers several advantages. First, it ensures high-quality prints with sharp and consistent images. Second, it allows for efficient printing of large quantities while maintaining cost-effectiveness. Moreover, offset printing is suitable for a variety of materials, including paper, cardboard, and even plastic. In contrast, other printing methods like rotogravure and photogravure rely on etched plates, making them more appropriate for specialized purposes such as packaging or high-volume magazine printing. Meanwhile, letter-press printing employs raised surfaces to transfer ink, but it lacks the versatility and precision of offset printing. In conclusion, the offset printing method effectively utilizes the immiscibility of water and oil to create high-quality and efficient prints. Its reliability and versatility make it a dominant choice in the modern printing industry.