When mud and water are combined, the result.

A. a mixture
B. a compound
C. an element
D. a molecule

When mud and water are combined, the result is a mixture. To understand why, let's break down the options given:

A. A mixture: A mixture is a combination of two or more substances that are not chemically combined. In this case, mud and water are physically mixed together but do not chemically react to form a new substance. Therefore, the result is a mixture.

B. A compound: A compound is a substance made up of two or more elements chemically combined in a fixed ratio. Mud is not a compound because it is not chemically bonded to water.

C. An element: An element is a pure substance made up of only one type of atom. Mud and water are both composed of multiple elements, so the result is not an element.

D. A molecule: A molecule is formed when two or more atoms are chemically bonded together. Water is a molecule because it consists of two hydrogen atoms bonded to an oxygen atom. However, mud is not a single molecule since it consists of a mixture of different substances.

Therefore, the correct answer is A. a mixture.