Fact 1: Carbon may be stored in sedimentary rock for millions of years.

Fact 2: Limestone is a type of sedimentary rock.

Given the two facts above, answer the question "What element can be stored in limestone for millions of years?" with the following options: 
- oxygen
 - Energy
 - matter
 - carbon
 - sodium
 - helium
 - rock salt
 - heat


 

    carbon     