Discretization is the work of dividing the range of values of a continuous attribute into intervals. Data cleaning includes processes of filling missing values, correcting inconsistencies, identifying outliers and getting rid of them. Huge amount of data makes mining data in coherent time impossible. Thus data reduction techniques are utilized. Reducing number of tuples, dimensionality reduction and etc. are utilized techniques for data reduction. Data integration merges data from different sources such as database, data flats etc. into a compatible data store. Data transformation includes the technique of aggregation, generalization, normalization and attribute construction. Therefore, the correct option is D.