Which one of the following does not come under the principle of selection and gradation?

The principles of selection and gradation in language teaching (as described by linguists like Palmer and Hornby) include: frequency (how often a word/structure occurs), availability (whether it is easily available when needed), coverage (the range of meanings a word covers), teachability, learnability, and similarity. Accuracy is not one of these principles—it is a goal of language learning, not a criterion for selecting items. Hence (1) is correct.