Sentences of a paragraph are given below in jumbled order. Arrange the sentences in the correct order to form a meaningful and coherent paragraph.

A. Nostalgia helps us maintain a positive psychological status when counteracting the negative impact of difficult situations.

B. Nostalgia is a sentimental longing for one's past.

C. The adaptive functions of nostalgia are many, with one effect being pain relief.

D. It is a self-conscious, perhaps bittersweet but predominantly positive social emotion.