Task: Question Answering
Input (English): Passage: Coming off their home win over the Bengals, the Texans flew to the Hubert H. Humphrey Metrodome for a Week 9 interconference duel with the Minnesota Vikings.  In the first quarter, Houston trailed early as Vikings RB Adrian Peterson got a 1-yard TD run.  The Texans responded with CB Jacques Reeves returning an interception 44 yards for a touchdown.  In the second quarter, Minnesota answered with QB Gus Frerotte completing an 8-yard TD pass to WR Sidney Rice and a 49-yard TD pass to WR Bernard Berrian. In the third quarter, Houston tried to rally as QB Sage Rosenfels completed a 3-yard TD pass to WR David Anderson.  In the fourth quarter, the Vikings replied with Frerotte completing a 25-yard TD pass to TE Visanthe Shiancoe.  The Texans tried to come back as Rosenfels completed a 14-yard TD pass to WR Andre Johnson.  However, the Vikings' defense stiffened for the win. QB Matt Schaub (21/29 for 224 yards and 1 interception), who started the game, left after the first half with a sprained left knee. 
Question: How many quarterbacks played in the game? 
Answer type: Number 
Output (English): 3.