The Pittsburgh Steelers opened their 2012 season facing the Denver Broncos, the team that had stunned them in the AFC Wildcard Playoffs to end their 2011 season.  The game was even more important, as it was former Indianapolis Colts quarterback Peyton Manning's first game with the Broncos, and his first since recovering from neck surgery following the 2010 season.  The Steelers were playing their first game with new offensive coordinator Todd Haley, but were missing long-time team leaders Hines Ward and James Farrior.  The first quarter of the game featured multiple punts by both teams, as neither offense could establish any consistency in moving the football.  The Steelers scored first, scoring on a 21-yard field goal to take a 3-0 lead early in the second quarter.  The Broncos would respond by going no-huddle and scoring the games first touchdown on a 7-yard run by Knowshon Moreno.  The Steelers would end the first half scoring on a 4-yard touchdown pass from Ben Roethlisberger to Heath Miller, giving them a 10-7 lead.  The Steelers would begin the third quarter by methodically driving the offense down the field and kicking a 35-yard field goal, capping off a drive that kept Manning and the Broncos offense on the sideline for nearly 10-minutes.  However, it would only take Manning 36-seconds to put the Broncos back on top 14-13, when a short screen pass to Demaryius Thomas resulted in a 71-yard touchdown.  The Steelers would put the first points of the fourth quarter on the board, when Roethlisberger found Mike Wallace for a 3-yard touchdown pass.  The Steelers would fail to convert on their 2-point conversion attempt, leading 19-14.  The Broncos would once again go no-huddle and score on a 1-yard pass to Jacob Tamme, and also convert a two-point attempt, giving the Broncos back the lead, 22-19.  After a 26-yard field goal with only 3-minutes remaining in the game, The Steelers were given one more chance to come back and win.  However, a Roethlisberger pass would be intercepted and returned 43-yards for a touchdown, sealing the Broncos win over the Steelers 31-19 as the team began their season 0-1 for the 2nd straight year.
Question: How many of the touchdowns were passing touchdowns?
Answer: 4