Sentence reordering
a) for their rulers / their best known / pyramids / perhaps / their / achievements are / tombs / built.
b) for / been preserved / stone structures / have / by/ the dry / the gigantic / climate / about 4,500 years.
- Perhaps their best known achievements are their pyramids tombs built for their rulers.
- The gigantic stone structures have been preserved for about 4500 years by the dry climate.