Hey there! I'm happy to help!
Agrarian civilization was basically the first big society, and it was focused on agriculture. Tons of people created crops and this created business, laws, power, etc.
Answers B, C and D to not seem to match this description. The best answer is A. people started to grow crops with specific harvesting cycles. Since agriculture helped make up civilization, it had to be very organized, and harvesting cycles would have helped accomplish this.
Have a wonderful day! :D