Question

the majority of the fossils found in indiana have been marine fossils. these include things like mollusks, coral, and clam relatives.
the existence of so many marine fossils here indicates that indiana was once covered by the ocean. in fact, the fossils are very old, from a time when much of north america was actually covered by the sea.
between then and now, the sea level fell, exposing
a a tsunami
b the inland sea
c hurricane patterns
d the continental shelf

Explanation:

The text states Indiana was once covered by ocean, and as sea levels fell, the previously submerged land that was part of the ocean's edge (continental shelf) would be exposed. The other options do not fit: tsunamis and hurricanes are weather events, and an inland sea would still be covered by water.

Answer:

D. the continental shelf