If Jakob Grimm, Who Developed What Has Come to Be

If Jakob Grimm, who developed what has come to be known as Grimm's law, were analyzing the historical relationships among the so-called dialects of Chinese (such as Cantonese and Mandarin) , what data would he be looking for in his linguistic fieldwork?

A) the characters used by people who spoke these different dialects
B) the average height, weight, and cephalic index of speakers of these several dialects
C) whether the speakers they surveyed knew any other non-Chinese languages
D) how the speakers of each dialect pronounce different words with similar meanings in the several dialects