Task: Inferred Class Relation Reasoning (ontology: Earth_Environment/EnvironmentOntology)

After reasoning, which of the following classes is one valid superclass of 'calcium atom'?

A. metal atom
B. mangrove biome sediment
C. EC 1.14.* (oxidoreductase acting on paired donors, with incorporation or reduction of molecular oxygen) inhibitor
D. methylamines

Answer: metal atom