Which of the following terms refers to synthetic materials made by humans?

The term "artificial" specifically refers to materials that are synthesized or created by humans, as opposed to those found naturally occurring in the environment. This designation highlights the fact that artificial materials are engineered for specific purposes, often utilizing various chemical and physical processes to achieve desired properties.

For instance, in the field of nanotechnology, artificial materials can be designed at the nanoscale to exhibit unique characteristics not present in their natural counterparts, such as enhanced strength, lighter weight, or specialized electrical properties.

In contrast, the other terms—natural, artistic, and biological—do not convey the notion of human-made materials. "Natural" pertains to materials that occur in nature without human intervention, "artistic" refers to materials involved in the creation of art, and "biological" relates to living organisms or life processes. Therefore, "artificial" is the most accurate term to describe synthetic materials developed through human ingenuity.