Simplify the following text for a Grade 12 native English-speaking person.
Original: In the spring of 1968 , National SDS activists led an effort on the campuses called `` Ten Days of Resistance '' and local chapters cooperated with the Student Mobilization Committee in rallies , marches , sit-ins and teach-ins , which culminated in a one-day strike on April 26 .
Simplified: In the spring of 1968 , National SDS activists led an effort on the campuses called `` Ten Days of Resistance '' and local chapters held rallies , marches , sit-ins and teach-ins , ending in a one-day strike on April 26 .