Which of the following materials is commonly used in 3D printing?

In the context of 3D printing, plastic is the most commonly used material due to its versatility, ease of use, and availability. Specifically, thermoplastics such as PLA (Polylactic Acid) and ABS (Acrylonitrile Butadiene Styrene) are popular choices in various types of 3D printers. These plastics can be melted and extruded through a nozzle to create complex shapes and structures layer by layer.

The properties of plastic, like being lightweight, strong, and capable of being easily shaped and melted, make it particularly suitable for a variety of applications, including prototyping, manufacturing, and even educational projects in a classroom setting. This prevalence of plastic in 3D printing is a significant reason it is the correct choice among the options provided.