Detailed Instructions: In this task, you're given an article and an answer. Your task is to generate the question for the answer based on the given article.
Q: Article: Watercolor is the oldest paints known. It dates back to the early cave men who discovered they could add lifelike qualities to drawings of animals and other figures on the walls of caves by mixing the natural colors found in the earth with water. Fresco , one of the greatest of all art forms, is done with watercolor. It is created by mixing paints and water and applying these to wet plaster . Of the thousands of people who stand under Michelangelo's heroic ceiling in the Sistine Chapel, very few know that they are looking at perhaps the greatest watercolor painting in the world. The invention of oil painting by the Flemish masters in the fifteenth century made fresco painting go down-hill, and for the next several centuries watercolor was used mainly for doing sketches or as a tool for study. It was not until the eighteenth and nineteenth centuries that English painters put back watercolor as a serious art form. The English have a widely-known love for the outdoors and also small, private pictures. The softness of watercolor had a remarkably strong attraction for them. The popularity of watercolor continued to grow until in the twentieth century. The United States passed England as the center for watercolor, producing such well-known watercolor artists as Thomas Eakins and Andrew Wyeth.
Answer: The start and development of watercolor.
A:
What is the passage mainly about?