How are proto-neurons thought to have evolved in early multicellular animals? a. through duplication of bacterial ion channel genes. b.through natural selection for increased speed of transmitting information. c.through mutation of bacteria ion channels. d.through horizontal gene transfer between early multicellular animals.

Which statement correctly describes other ways in which nebulae and stars are different? a. a star always has a higher density than a nebula. b. stars can form inside a nebula but a nebula can never be produced by any star. c. stars can never form inside a nebula but a nebula can be produced by any star. d. a nebula always has a higher density than a star. reset submit