Choose the word/ phrase (A, B, C or D) that best fits the blank space in the following passage.      

    The changes that took place in schools have changed the roles of teachers. In the past, teachers (19) ______ the major source of knowledge, the leader and educator of their students' school life. Nowadays, teachers provide information and show their students (20) ______ to handle it. Although they are still considered to be a kind of facilitator in the class, they can be thought of as a facilitator in the learning process. Another difference between the past and present tasks of teachers is represented by the (21) ______ background they need in order to be able to use computers and some other machines effectively. Instead of teaching with chalk, they need to be information technology experts.             One of the biggest challenges (22) ______ teachers is that their role in the school management has also changed. The school needs them as individuals, who can make (23) ______ and cope with the stress of the world of schools. At the same time teachers need to be able to work in teams, and cooperate with colleagues and parents. A teacher has not only to instruct but also to (24) ______ the students with confidence and determination.

 In the past, teachers (19) ______ the major source of knowledge, the leader and educator of their students' school life.