The Wisconsin Department of Transportation reports seven semi-trucks and 33 cars were involved in a chain reaction crash on Interstate 94 Sunday shortly after noon.  One person was critically injured and seven others required medical treatment.  State officials were warning drivers to be careful because the snow was creating slick road conditions.  Traffic was routed off the Interstate while the injured were removed and the scene was cleared.  That stretch of I-94 in western Wisconsin was reopened to traffic several hours later.