用恰当的引导词填空并体会它们的功能。
1. Through comparison, he found that the locations of the 117 known Maya cities correspond to the positions of the stars.
2. What is most extraordinary about these complex structures is how they were built without the use of wheels, metal tools or even animal power.
3. The fact that Maya society was technologically primitive makes its achievements all the more incredible and mysterious.
4. But the greatest mystery of all is what caused the Maya to abandon most of their great cities.
5. Why Maya civilization collapsed remains a mystery.
