The professor in the lecture using evidence illustratesthat none of the three theories in the reading passage explaining the functionof Chaco Canyon is convincing. 

The evidence disproving the first theory thatthe Chaco structures were residential is that there are few fireplacesfor cooking inside. 

The second theory contending that the Chacostructures were used to store food like grain maize is still notconvincing. 

請教,這三句話是不是存在頭重腳輕的問題（主語太長）?V-ing做插入語到底應(yīng)該怎么用?語感好差啊!