Which of the following constitutes one of the four tasks of mourning?

Accepting loss is one of the four tasks of mourning as defined by grief theorists, such as William Worden. This task involves acknowledging the reality of the loss and the associated feelings that come with it. It is essential for individuals to confront their grief rather than avoid it, as acceptance allows for the integration of the loss into their ongoing life experiences.

When a person accepts the loss, they begin to process their emotions and start to rebuild their identity and life without the deceased. This task facilitates healing and helps individuals move forward while still honoring the memory of what they've lost. In essence, it is a critical step toward finding peace and navigating the feelings surrounding grief.

The other options, such as denial of reality, resisting change, and separation from memories, do not align with the healthy progression through the grieving process, as they can impede acceptance and prolong suffering rather than assist in recovery.