Patent US 4,135,314

A magnetic audio tape comprising at least two tracks in one direction of advance of the tape is applied for recording with sounds of a sentence for study. The sentence has at least two blank parts each of which can constitute a question for an expected answer, wherein one track of the tape is recorded with the sound of the sentence except for the one blank part of the sentence and the other track of the tape is recorded with the sound of the sentence except for the other blank part of the sentence. The same sound of the sentence recorded on all of the tracks coincides with each other to be reproduced as a single sound when these tracks are scaned at the same time by magnetic head or heads of a tape recorder.