If engineers require a material that can be stretched and reduced in cross-section without breaking, they would choose a material that is:

The correct answer is ductile because ductility refers to a material's ability to undergo significant plastic deformation before fracture. This means that a ductile material can be stretched and reduced in cross-section without breaking, making it ideal for applications where flexibility and the capacity to absorb stress are necessary.

Ductile materials are typically metals like copper and aluminum, which can be drawn into wires or hammered into sheets, showcasing their ability to maintain integrity under stress while changing shape. This property is essential in engineering and manufacturing processes, where materials must endure various forces and still maintain their functionality.

In contrast, while elastic materials can stretch and return to their original shape, they do not permanently deform like ductile materials do. Brittle materials, on the other hand, tend to break or shatter under stress, making them unsuitable for applications requiring stretching. Plastic materials generally refer to non-metal substances that can be molded but don't necessarily possess the same levels of stress resistance or ductility as metals.