In the past, teachers used to be the (1) ________ source of knowledge, the leader and the educator of their students' school life.Đoạn văn1/40Read the following passage and mark the letter A, B, C, or D to indicate the correct option that completes each of the blanks. In the past, teachers used to be the (1) ________ source of knowledge, the leader and the educator of their students' school life. largemajorseriousfirstGiải thíchB. major