Read the passage from Animal Farm. On Sundays there was no work. Breakfast was an hour later than usual, and after breakfast there was a ceremony which was observed every week without fail. First came the hoisting of the flag. Snowball had found in the harness-room an old green tablecloth of Mrs. Jones's and had painted on it a hoof and a horn in white. This was run up the flagstaff in the farmhouse garden every Sunday morning. The flag was green, Snowball explained, to represent the green fields of England, while the hoof and horn signified the future Republic of the Animals which would arise when the human race had been finally overthrown.

What is the central idea of this passage?

Sundays are days of rest and ceremony on the farm.
Snowball tries to convince everyone that England is green.
Sundays are dedicated to planning how to overthrow humans.
Snowball is becoming more and more like those he despises.