What are the four subgroups of language in the balto-slavic family? ap human geo?

The Balto-Slavic languages are a branch of the Indo-European family of languages. It traditionally comprises the Baltic and Slavic languages. Baltic and Slavic languages share several linguistic traits not found in any other Indo-European branch, which points to a period of common development. Most Indo-Europeanists classify Baltic and Slavic languages into a single branch, even though some details of the nature of their relationship remain in dispute in some circles, usually due to political controversies. Some linguists, however, have recently suggested that Balto-Slavic should be split into three equidistant groups: Eastern Baltic, Western Baltic (which is extinct) and Slavic.

A Proto-Balto-Slavic language is reconstructable by the comparative method, descending from Proto-Indo-European by means of well-defined sound laws, and out of which modern Slavic and Baltic languages descended. One particularly innovative dialect separated from the Balto-Slavic dialect continuum and became ancestral to the Proto-Slavic language, from which all Slavic languages descended.