Which of the Following Would Be an Acceptable Research Topic

Which of the following would be an acceptable research topic in the field of historical linguistics?

A) Whether or not the speakers of Apache and Navajo once spoke a common language
B) Whether or not Apache and Navajo speakers use the same body language to signal gender differences
C) Whether or not Apache and Navajo speakers organize their languages using the same syntactical structures
D) All the features of a given language as it is spoken at a particular point in time
E) Frame substitution to investigate the syntax of a particular language