Answers:

1. Druids differed from the military class because they didn't go to war, didn't pay tributes and they had an exemption from military service.

2. They studied for twenty years.

3. They wrote in Greek for two reasons: the first was that they didn't want their doctrines to be divulgated among the mass of the people, the second was that if they had relied on writing their tales and their stories, they would have lost the employment of  their memory.

4. They taught the young people to respect the stars and their motion, the extent of the world and of our earth, the nature of things, the power and the majesty of the immortal god.