Answer based on context:

Coming off their interconference home win over the 49ers, the Steelers flew to University of Phoenix Stadium for an interconference duel with the Arizona Cardinals. Near the end of the first quarter, Pittsburgh delivered the first punch as QB Ben Roethlisberger completed a 43-yard TD pass to WR Santonio Holmes for the only score of the period. However, after a scoreless second quarter, the Cardinals responded with back-up QB Kurt Warner completing a 6-yard TD pass to WR Jerheme Urban for the only score of the period. In the fourth quarter, things went wrong for the Steelers as Arizona took the lead with WR Steve Breaston returning a punt 73yards for a touchdown, while RB Edgerrin James got a 2-yard TD run. Pittsburgh tried to mount a comeback as Roethlisberger and Holmes hooked up with each other again on a 7-yard TD pass. However, the Steelers' final drive ended with an interception.

How many touchdowns did Ben Roethlisberger throw to Santonio Holmes?
2