The correct answer is: A. Signal
A sand hump is a substitute to signal and also a means of isolation. It is a type of sand dune that forms when wind blows sand over an obstacle, such as a rock or a tree. The sand builds up around the obstacle, creating a mound that can be several meters high. Sand humps can be found in many parts of the world, including deserts, beaches, and even in some urban areas.
Sand humps are important because they can help to protect plants and animals from the wind. They can also help to trap water, which can be used by plants and animals. Sand humps can also be used as a means of isolation. For example, they can be used to create a barrier between two different areas, such as a residential area and an industrial area.
The other options are incorrect because they are not substitutes for signals or means of isolation. Signal is a term used to describe a message or a piece of information that is sent from one place to another. Signal overlap is a term used to describe the situation when two or more signals are sent at the same time, which can cause interference. Over signal is a term used to describe a signal that is too strong, which can cause distortion.