题目内容：
阅读下列短文，回答题。Mexico's neighbours are the United States to the north and Guatemala and Belize to the south.
Mexico is about one quarter of the size of the United States. Mexico has more than ninety million people. The language of Mexico is Spanish. This makes Mexico the world's largest Spanish-speaking country.
Mexico City is the capital and largest city of Mexico. The city is also above the sea level very high. It is 7,349 feet (2,240 metres). This makes it one of the highest capital cities in the world.
The population, of Mexico City grows bigger every day. About thirty million people live there. It has more people than any other city in the world, even more than Tokyo.
Mexico also has its specialities. Many of the foods we eat started in Mexico. Foods like beans,maize, avocados, tomatoes, peanuts, chili peppers, vanilla, and chocolate come from Mexico. Mexico is also famous for its cactus (仙人掌) plants. Mexico has more kinds of cactus than any other country.
Mexico is __________ the USA. A．to the south of
B．on the north of
C．a part of
D．as large as
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