A Wonderleaf question

a real page from the book
No single inventor can be named. The earliest known wheels for carts appear around 3500 BCE in Mesopotamia, in what is now Iraq, and they likely came from many careful makers improving wood, axles, and carts over time.
The clever part was not noticing that round things roll; children notice that in a minute. The leap was holding a turning wheel beneath a load, then letting an axle carry the weight. Later, spokes made wheels lighter enough for faster travel.
Roll a toy or can across the floor, then slide it, and compare which way moves more easily.
Watercolour scenes, straight answers, about three minutes cover to cover.
Open the picture bookOne more wonder: Why is space so dark?
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