שאלה | How can data leakage be prevented during feature engineering/transformation?

How can data leakage be prevented during feature engineering/transformation?

		By using a different feature engineering/transformation technique for each fold of the dataset.
		By transforming features without considering their relevance to the target variable.
		By including all features from the validation set in the training set.
		By ensuring that feature engineering/transformation is performed only on the training set, without using information from the validation or test set.