Despite the differences, it is possible for paraphrasing and coreference to co-occur, as in the case of b and d. NLP components dealing with paraphrasing and coreference seem to have great potential to improve understanding and generation systems.
they have been the focus of a large amount of work in the past couple of decades (see the surveys by Androutsopoulos and Malakasiotis [2010], Madnani and Dorr [2010], Ng [2010], and Poesio and Versley [2009]).