How do fraternal twins form? a- two eggs are fertilized by one sperm b- two sperm fertilize an egg c- a fertilized egg splits in two d- two eggs are fertilized by two sperm

Why should the united state be concerned about air pollution in china?

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.

Explain how paleontologists use trilobite fossils as index fossils for various geologic time periods.