Very powerful volcanic eruptions send large amounts of ash high into the atmosphere, blocking sunlight and causing abnormally cold temperatures for a year or more after the eruption. In 44 B. C. there was a powerful eruption of Mount Etna in Sicily. In the following year, Chinese historians recorded summer frosts and dimmed sunlight in China, thousands of miles east of Sicily. If these phenomena were caused by volcanic ash in the atmosphere, then the ash sent into the atmosphere by Mount Etna' s eruption must have spread over great distances. In evaluating the support given for the conclusion advanced in the last sentence of the passage, it would be most important to determine whether ["there were any volcanic eruptions near China around the time of Mount Etna's eruption", 'modern monitoring equipment can detect the precise path of volcanic ash in the atmosphere', 'the abnormal weather in China lasted for a full year or longer', 'subsequent eruptions of Mount Etna were as powerful as the one in 44 B. C.']