The correct answer is the combination of a metal with another element.
An alloy is a combination of two or more metallic elements to make a stronger material. For instance, there are bronze alloys, brass alloys, and coin alloys.
We can confirm that an alloy is a combination of one metal with another metal because stainless steel is made of an iron and chromium alloy (iron is a metal; chromium is also a metal). Therefore, we can confirm that option C is the best choice.