An American professor who has studied the Mayas has come up(1)_____ a new theory about the sudden end of their empire. According to Professor Richard Hansen, an archaeologist(2)____ the University of California; the collapse of the Mayan(3)____ in Central America was(4)____ about by the Mayas(5)____.
Their object was to display their wealth and power by making their buidings and decoration as beautiful as(6)____. This involed using large quantitiles of lime, which they put(7)____ the walls to make them smooth. Unfortunately, the creation of lime is a process which requires intense heat, and they(8)____ had to cut down huge number(9)_____ trees. This affected the quatily of the soil, and it(10)_____ almost impossible to farm.

1.a.with            b.to            c.for          d.about
2.a.in                b.at             c.on             d.belongs to
3.a.civil           b.civilans         c.civilize             d.civilization
4.a.brought          b.turned         c.came             d.made
5.a.themselves          b.themself           c.theirself           d.theyself
6.a.popular           b.suitable               c.possible               d.available
7.a.in                b.on             c.for             d.to
8.a.however            b.therefore             c.moreover            d.besides
9.a.on              b.of              c.for               d.ko chọn
10.a.become             b.becomes                c.has become              d.became