完形填空

　　Mexico, the largest nation in the region, is a good example of life in Middle America．Although Mexico is a large country, 　　1　　 12 percent of its land is good for farming．　　2　　 40 percent is good grassland．The rest of the land is hills and mountains, 　　3　　 plateaus(高原), or wet coastal regions．

　　The mountains are too 　　4　　 to farm．The high plateau in the middle of Mexico would be good farmland if it had more 　　5　　．The coastal areas receive so much 　6　　 that the land 　　7　　 becomes waterlogged(浸满水的)．For all of these 　　8　　, Mexicans must 　　9　　 the good farmland they have．　　10　　 good farming has not always been 　　11　　 in Mexico．For many 　　12　　, Mexican farmers had 　　13　　 traditional crops．These 　　14　　 corn, beans, and squash(南瓜)．　　15　　, when the Spanish arrived in the 1500's, they tried to 　　16　　 new ideas．They thought new 　　17　　 such as onions, turnips, sugarcane, and bananas would 　　18　　 well in warm tropical(热带的)　　19　　．But the Mexicans wished to continue with their old 　　20　　．

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