11 people were injured in a chain-reaction crash in a work zone in Redwood County yesterday morning.  The state patrol says it happened at 11:14 a.m. on Highway 71 in Redwood Falls Township south of Redwood Falls.   Three vehicles were all northbound when they stopped for a MNDOT flagger.  A fourth vehicle was slowing when it was rear-ended by a semi, which cause all the waiting vehicles to collide with each other.   10 of the victims suffered non-life-threatening injuries and were taken to the Redwood Falls Hospital.   They ranged in age from 2-years-old to 79-years-old.   Five of the victims were age 15 or younger.  One of the vehicle drivers, 92-year-old Mary Ann Olson of Redwood Falls was airlifted to North Memorial Hospital with life-threatening injuries.   The only person to escape injury was the semi driver, 53-year-old Jay Klabunde of Windom.