A group of dogs is pulling a sled over snow as the sun sets .
A group of dogs are pulling a sled over snow as the sun sets .
A group of dogs is pulling a sled over snow as the sun sets.
A group of dogs are pulling a sled over snow as the sun sets.
If the group of dogs is pulling a sled, then they are pulling.
If the group of dogs is pulling a sled , then they are pulling .