Explanation:
Index fossils are fossils type fossils that are used to identify stratigraphic records and their positions. They are vey key in determining relative ages of rock sequences.
- These fossils have a short vertical stratigraphic range.
- Index fossils have short evolutionary history.
- They are widely distributed in nature.
- Examples of index fossils are trilobites and ammonites.
C is the answer. The people (wife and husband) studied and realized that their beak was unique
<span>DNA helicases break the hydrogen bonds in the DNA molecule</span>