缺词填空

      The USA has a much bigger population （人口）than Australia, and A_1_ cities are m_2_ crowded than Australian o_3_. There are not so many mountains in Australia as in the USA. Both countries have

deserts and beautiful b_4_. But America has many more rivers than Australia. The northern and central

parts of the USA h_5_ much more snow in winter than a_6_ in Australia and generally these two areas

have a colder w_7_ than Australia does. Australia is in the southern hemisphere（半球） and doesn’t

have its winter at the same time a_8_ countries in the northern hemisphere. Most people in these countries s_9_ the same language ---English, but their accents(口音) are very d_10_.

生产石膏的主要原料是（）

A.CaCO3

B.Ca（OH）2

C.CaSO4•2H2O

D.CaO