The landform that best describes lowest elevation or is most clearly associated with it is:

A. Plains

B. Plateaus

C. Mountains

A. Plains

Explanation:

Plateaus are high plains or "tablelands" meaning they are elevated. Mountains are also generally elevated environments. By process of elimination, the answer is plains. However, we can prove this by looking at the definition of a plain; it is as follows:

"A large area of flat land with few trees."

Its synonyms include words like "lowland"