The correct answer is A.
The Apriori property states that if a set cannot pass a test, its supersets will also fail the same test. This means that if a set of items is not frequent, then any superset of that set will also not be frequent. This property can be used to prune the search space in frequent item set mining, which can improve the efficiency of the algorithm.
Option B is incorrect because level-wise generation of frequent item sets does not decrease the efficiency of the algorithm. In fact, it can improve the efficiency by reducing the number of candidate sets that need to be evaluated.
Option C is incorrect because level-wise generation of frequent item sets does not improve the efficiency of the algorithm. In fact, it can decrease the efficiency by increasing the number of candidate sets that need to be evaluated.
Option D is incorrect because if a set can pass a test, its supersets may or may not pass the same test. This is because the support of a set is not necessarily equal to the support of its supersets.