Q: Fact 1: Carbon may be stored in sedimentary rock for millions of years. Fact 2: Limestones are a common type of sedimentary rock. Given the two facts above, what may be stored in limestone for millions of years?

OPT:
I. dark matter;
II. chemicals;
III. still-living organisms;
IV. nothing;
V. fossils;
VI. matter;
VII. carbon;
VIII. Energy;
The answer is:
VII.