Concept:Sand or dust ablution is known as tayammum in Islamic law.Explanation:When water is unavailable or cannot be used, a Muslim may perform tayammum.This involves striking clean sand or dust with the hands and wiping the face and hands.The other options are incorrect: tashahhud is the testimony recited in prayer, wudu is ablution with water, and tahara means purity in general.Answer:B. tayammum