Over time multitudinous special-rate forms have gradually developed either because of unique cost factors or to generate certain patterns of shipment. Fundamentally, these special rates materialise as a class, exception, or commodity rate." Cited in Engelbrecht & Ramgovind (2020). Explain any two categories where the special rates can be grouped. (Note: One mark for the category and four marks for the explanation) (Hint: Support your explanation with examples.