Question

which phrase describes organisms that formed index fossils?
are extinct
had soft parts
were generally large
lived in a narrow geographic area

Explanation:

Index fossils are fossils of organisms that are used to define and identify geologic periods. These organisms must have been widespread geographically, existed for a relatively short period of geologic time, and are now extinct. Soft - bodied organisms are less likely to form fossils (as they don't preserve well). Organisms that formed index fossils were not necessarily large. And they were not limited to a narrow geographic area (they were widespread).

Answer:

are extinct