Article Photos: Oklahoma football: QB platoon appears to be a last resort 1/3

Oklahoma University quarterbacks Blake Bell, right,  and Trevor Knight  warm up at a preseason NCAA college football practice in Norman, Okla. on Friday, Aug.  2, 2013.  (AP Photo/Tulsa World,  Matt Barnard)  ONLINE OUT; TV OUT; TULSA OUT  ORG XMIT: OKTUL101