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.