Final answer:
Dave, who immediately questioned his advanced cancer diagnosis and sought a second opinion, is exhibiting the reaction of denial, which is the first stage in the Kübler-Ross five-stage model of grief.
Step-by-step explanation:
When Dave was told by his doctor that he was in the advanced stages of cancer and he immediately questioned the report and sought a second opinion from another doctor, Dave is exhibiting the reaction of denial. This reaction is part of the five-stage model of grief developed by Elizabeth Kübler-Ross. Dave is not willing to believe that he is dying, which is a common characteristic of the denial stage. This is the initial response that many individuals have when faced with the prospect of dying, and it is one stage that people may go through as they come to terms with their terminal illness.