Which of the following statements about higher$-$order functions is true?

a$.$

They are special functions that ignore program scope and have access to localized variables.

b$.$

They allow the definition of specialized ordering logic for data sets.

c$.$

They are mutators that can be utilized on functions to remove redundant patterns in code.

d$.$

They separate the task of transforming data values from the logic of accumulating the results.