Which of the following represents the posterior opening of the digestive system?

The posterior opening of the digestive system is represented by the anus. The digestive system is organized in a way that involves a continuous tube which processes food, starting from the mouth and ending at the anus. The anus serves as the final part of this system, allowing for the expulsion of waste material after the digestion and absorption processes have taken place. The term "posterior" refers to the location of the anus at the end of the digestive tract, making it the correct choice in identifying the posterior opening.

The other options are involved in the digestive process but are located anteriorly in the system. The mouth is where ingestion occurs, the esophagus acts as a passageway for food to reach the stomach, and the stomach is responsible for digesting the food further. None of these serve the function of expelling waste, which is specifically performed by the anus.