How do historians know so much about the religious lives of the Sumerians?

Can someone read this article and tell me the 1) key ideas and 2) one key quote (copy and paste the link the article is not to long at all)from

About political condition and history of nepal

According to ohrp, a problem is an “unanticipated problem” when it meets which of the following criteria: unexpected, related or possibly related to the research, suggests that the research does not put the subjects or others at greater riskunexpected, related or possible related to the research, suggests the research puts subjects or others at greater riskunexpected, unrelated to the research but still occurring with a subject, suggests the research puts others at greater riskexpected, related or possible related to the research, suggests the research puts others at greater risk