O who lives in a pineapple under the sea HELP MEEE

Why should Europe be concerned with changes in population trends?

Based on the cause-and-effect relationship in this sentence, what is the meaning of the word revert? the brownies kali made using a new recipe were too dry, so she reverted to her original recipe. a) to alter or change completely; revise b) to dispose of or remove; to throw away c) to prepare for something; assemble or make d) to go back to a previous state or practice