In the following passage, some of the words have been left out. Read the passage carefully and select the correct answer for the given blank against the number given out of the four alternatives.

_____(1)______ it became difficult to empirically prove that children _____(2)______ better in private schools, the attack _____(3)______ a new weapon per unit cost of learning outcomes. Most of the learning outcome researches almost _____(4)______ fail to understand the entire _____(5)______ of education in any depth and reduces it to learning of so-called 3Rs for economic purposes.