Sentence:  Since the writer had not noticed this characteristic in married students scattered throughout the various sections previous to this experiment , nor , as a matter of fact , in those who were continuing in `` single sections '' , he can only conclude that there must have <WSD>been</WSD> something `` contagious '' within the specific group which caused this to occur . 
Meaning of the word marked with <WSD> tags:  happen, occur, take place; this was during the visit to my parents' house"