The correct options are
A Relation of a population to its environment
B Relation between a species and its environment
The study of the interactions between living things and their environments is known as ecology. In ecology, everything is connected to everything else and there is a constant interaction between organisms and their environment. Autecology & Synecology are two main branches of ecology. Autecology is the study of individual organism or individual species. It is also known as population ecology. Synecology is the study of group of organisms of different species which are associated together as a unit in form of a community. Also known as community ecology. Autecology helps us to understand the relationships between a particular organism and environment. Synecology helps us to understand the relationships between communities and environment.