Which is a comma splice? Two great ballet dancers began their careers in St. Petersburg, they were Anna Pavlova and Vaslav Nijinsky.

Anna Pavlova and Vaslav Nijinsky, both great ballet dancers, began their careers in St. Petersburg.

Two great ballet dancers, Anna Pavlova and Vaslav Nijinsky, began their careers in St. Petersburg.

The great ballet dancer Anna Pavlova began her career in St. Petersburg, as did Vaslav Nijinsky, another great dancer.