The correct answer is: a) Natural mineral pigments and cloth canvas.
Thangka paintings are Tibetan Buddhist paintings that are traditionally made on cloth canvas with natural mineral pigments. The canvas is usually made from cotton or wool, and the pigments are made from ground minerals, such as lapis lazuli, malachite, and cinnabar. Thangka paintings are often very colorful and detailed, and they can be used for a variety of purposes, such as religious worship, meditation, and education.
Option b) is incorrect because oil paints are not typically used for thangka paintings. Oil paints are made from a mixture of oil and pigment, and they take a long time to dry. This makes them unsuitable for use on cloth canvas, which can stretch and warp over time.
Option c) is incorrect because watercolors are also not typically used for thangka paintings. Watercolors are made from a mixture of water and pigment, and they are not as durable as oil paints. This makes them unsuitable for use on cloth canvas, which can be easily damaged by water.
Option d) is incorrect because acrylic paints are a modern invention, and they were not available when thangka paintings were first created. Acrylic paints are made from a mixture of acrylic resin and pigment, and they are very durable. However, they are not typically used for thangka paintings because they do not have the same rich colors and textures as natural mineral pigments.