Whats the most important idea of practical value in the data preparation steps of data mining from the choices listed below?

A. The most important idea of practical value in the data preparation steps of data mining is the use of domain knowledge while organizing, selecting, formatting, cleaning, and understanding the data sets; keeping in the forefront, the context in which the data set is used, based on familiarity with organizational goals and processes in the domain from which the data is derived. B. The most important idea of practical value in the data preparation steps of data mining is variable selection and the need to weed out data having no effect in forming any worthwhile predictive behavior. C. The most important idea of practical value in the data preparation steps of data mining is sampling from the database-performing analysis based on a subset of the data provided, and ensuring that rare events are not over sampled. D. The most important idea of practical value in the data preparation steps of data mining is taking care to pre-process and clean the data so the formatting is easily recognized by the data mining engine. E. The most important idea of practical value in the data preparation steps of data mining is dealing with outliers and missing data records.