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 been something `` contagious '' within the specific group which <WSD>caused</WSD> this to occur . 
Meaning of the word marked with <WSD> tags:  give rise to; cause to happen or occur, not always intentionally