Which of the following probably happened first? Indo-European groups migrated to different parts of Europe and Asia. The Indo-European people lived in north-central Europe. Invading groups conquered existing civilizations. Many related languages were spoken throughout the world.

What is the significance of the protein-lined pits? a. protein attracts other proteins needed for atp synthesis within the cell. b. protein-lined pits are able to transport one molecule at a time down the concentration gradient within the cell. c. the polarity of proteins allows other polar molecules to attach and be transported in the cell by transport channels. d. receptors within the pits allow ligands to fuse and be transported into the cell by endocytosis.