To answer this question, you need to have an understanding of the different model types in Cognos 8.
Option A) OLAP and DMR - This option is incorrect because OLAP is not a model type in Cognos 8. DMR (Dimensionally Modeled Relational) is a valid model type, but it is not the only model type available.
Option B) Dimensional and DMR - This option is incorrect because although DMR is a valid model type, "Dimensional" is not a model type in Cognos 8.
Option C) Relational and SAP BW - This option is incorrect because SAP BW is not a model type in Cognos 8. Relational is a valid model type, but it is not the only model type available.
Option D) Relational and Dimensional - This option is correct because the two distinct model types that authors can work with in Cognos 8 are Relational and Dimensional. Relational models are based on traditional relational databases, while Dimensional models are based on multidimensional structures such as star schemas or snowflake schemas.
Therefore, the correct answer is D) Relational and Dimensional.