Sentence:  Some 80 reaction tubes from 13 manifold fillings were illuminated in the temperature range from 40 to 85 ` in a further endeavor to determine the <WSD>cause</WSD> of the irreproducibility and to obtain information on the activation energy and the effect of light intensity . 
Meaning of the word marked with <WSD> tags:  any entity that produces an effect or is responsible for events or results