From the passage we understand that Carl Sagan writes （）

A．One of the major tasks of education is to discover the most promising students.
B．In order to teach effectively, educators are requested to lay emphasis on one particular field.
C．Some subjects have been over-emphasized in public schools.
D．The progress of the society cannot merely rely on inventors.

A．students should learn more up-to-date knowledge
B．lack of scientific knowledge will lead to poor relations between producers and users of scientific services
C．students are getting to know the importance of a good balance among the branches of knowledge
D．sufficient attention should be given to bask knowledge