Which of the following features are correct? Choose correct option. a. Natality refers to the number of births in a population during a given period. b. Mortality refers to the number of deaths in a population during a given period. c. Immigration is the number of individuals of the same species that have come into the habitat from elsewhere during a given period. d. Emigration is the number of individuals of the same species that have left the habitat and gone elsewhere during a given period.