Third in a series: With no acknowledged successor in line to take control, the junior from Arkansas finally gets his first real opportunity to become USC’s starting quarterback.

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USC opens spring practice Saturday and plenty of attention will be focused on the quarterbacks, as four main competitors seek to replace Mark Sanchez as the Trojans’ starter. The Times’ Gary Klein had question-and-answer sessions with each of the contenders as they prepared to vie for the starting spot. Today, he summarizes his interview with Mitch Mustain, a junior who has the most game experience of the group.