Question

read the text.
before humans developed written language, they created pictures on rocks. this
ock art\ often portrays animals or abstract designs. the pictures could have been records of events, plans, or messages. there are two basic types: pictographs and petroglyphs. pictographs were drawn or painted on the surface of rocks with pigments such as charcoal, blood, or chalk. petroglyphs, on the other hand, were scratched or carved into the rock itself. with some petroglyphs, only the surface layer of rock is removed, showing a lighter color of rock beneath the outer layer. other petroglyphs consist of carvings cut deep in the rock. most pictographs have faded, while petroglyphs have endured longer.
which organizational structure does this text primarily use?
problem - solution
compare - contrast
sequential

Explanation:

The text introduces two types of rock art, pictographs and petroglyphs, then details their differences in creation method, materials, and durability, using "on the other hand" to signal the comparison of their contrasting traits.

Answer:

compare-contrast