The correct answer is: Both fresco and tempera.
Fresco is a technique of mural painting executed on wet lime plaster. The plaster is applied in two or more layers, the first being a rough layer called the arriccio, and the second, a smooth layer called the intonaco. The artist works on the intonaco while it is still wet, applying pigments mixed with water. As the plaster dries, the pigments become chemically bonded to the plaster, creating a permanent image.
Tempera is a painting medium made from pigments mixed with a water-soluble binder, usually egg yolk. Tempera paintings are typically characterized by their matte finish and their ability to retain their colors over time.
Both fresco and tempera were used in the creation of monastery murals. Fresco was the preferred technique for large-scale murals, as it allowed for a quick and fluid application of paint. Tempera was often used for smaller murals and for details in fresco paintings.
Gouache is a type of opaque watercolor paint. It is made from pigments suspended in gum arabic, and it dries to a matte finish. Gouache is often used for illustration and for painting on paper. It was not commonly used in the creation of monastery murals.