Reference:
The eval command is used to create new fields or modify existing fields based on an expression2. The output of an eval expression is a calculated field, which is a field that you create based on the value of another field or fields2. You can use calculated fields to enrich your data with additional information or to transform your data into a more useful format2. Therefore, option B is correct, while options A, C and D are incorrect because they are not names of knowledge objects that represent the output of an eval expression.