Available choices: [I] abrasion. [II] fossils. [III] an anion. [IV] acid. [V] nitrogen. [VI] gypsum. [VII] carbon. [VIII] NaCl.

Fact 1: Carbon may be stored in sedimentary rock for millions of years. Fact 2: Limestone is a rock composed of calcium, carbon and oxygen. Given the two facts above, what is in limestone?
Answer:
[VII]