Question: How many teams were represented in the pair of motor races held on 18 and 19 April 2015 at the Bahrain International Circuit in Sakhir, Bahrain?
Sentence (from "2014 Bahrain GP2 Series round"): The first race, a 32-lap feature event, was won by ART Grand Prix driver Stoffel Vandoorne after starting from second position.
Relevant evidence: No