Comma is required before whereas:
e.g Most high school students wear uniforms in Japan, whereas very few do in Canada.

knights - European soldiers who fought on horseback centuries ago.
ancestors - family members who lived in past times
medieval - relating to the Middle Ages in Europe (about A.D. 500~1500)

1. Rat
2. Ox
3. Tiger
4. Rabbit
5. Dragon
6. Snake
7. Horse
8. Goat
9. Monkey
10. Rooster
11. Dog
12. Boar

Subjunctive:

S+ wish that S + were/would + ...