Sentences of a paragraph are given below in jumbled order. Arrange the sentences in the correct order to form a meaningful and coherent paragraph.

A. Metal detectors are useful for finding metal hidden within objects or metal objects buried underground.

B. Metal detector is an electronic instrument that detects the presence of metals nearby.

C. If the sensor comes near a piece of metal, this is indicated by a changing tone in earphones or a needle moving on an indicator.

D. They often consist of a handheld unit with a sensor probe that can be swept over the ground or other objects.