Which of the following is an opposite of "a bummer"?

The term "a bummer" typically refers to a disappointing or unfortunate situation. Therefore, its opposite would be something that brings happiness or a positive experience. A "pleasant surprise" fits this definition perfectly, as it denotes an unexpected, enjoyable occurrence that brings joy rather than disappointment. This makes it the correct answer, as it directly contrasts the negative connotation of a bummer by implying something uplifting and favorable.

In contrast, the other options convey meanings aligned with disappointment or negative outcomes. "A disappointment" is directly related to the feeling of being let down, while "a setback" suggests a hindrance or obstruction in progress, and "a misadventure" implies an unfortunate or amusing incident that usually has negative implications. Thus, they don’t serve as opposites to "a bummer."