A．Whether some languages share the common ancestor.
B．Whether a language is in the process of dying out.
C．When a certain language came into existence.
D．Why sister languages exist in the same region.
A．She is not sure what causes languages to change.
B．She does not think that languages change quickly.
C．She thinks the fact she just mentioned might be hard to believe.
D．She thinks languages evolved differently in the past than they do now.
A．The difference in age among American mountain ranges.
B．The importance of a technique used for dating.
C．The recent discoveries about a mountain range.
D．A comparison of various minerals used for dating.
A．A desert that once connected two continents.
B．An ancient lake located in the American Southwest.
C．Sands carried by a river from the Appalachian Mountains.
D．A nearby mountain range that had flattened out over time.