What type and rating of fire extinguisher is legally required to be carried on a commercial passenger bus in Alberta?

1. A water-based extinguisher rated at least 2-A
2. A dry chemical extinguisher with a rating of at least 2-A:10-B:C
3. A CO2 extinguisher rated at least 5-B
4. No extinguisher is required for passenger vehicles under 24 seats