Serena Goes to See a Psychologist Who Specializes in Helping

Serena goes to see a psychologist who specializes in helping people with mild depression. Serena expresses that she would like to feel "happier." Which of the following activities should elevate Serena's mood, at least for a few weeks?

A) asking for a promotion at work
B) making one new friend a day for a month or more
C) writing a letter to someone expressing both positive and negative feelings about past events
D) expressing gratitude to someone who has helped her