Which of the following are types of supporting materials? _testimonials _illustrations _explanations _all of the above _none of the above

Testimonials, illustrations and explanations are all supporting materials. So the answer is all of the above.

sumerians were responsible.

nothing certain is known about what happened, but it seems that the country declined gradually, perhaps due to bad government, or, more likely, due to a series of bad harvests, which resulted in widespread and recurrent famine.