题目内容
阅读下列短文，掌握其大意，然后从各题所给的四个选项（A、B、C和D）中，选出最佳选项．
In some parts of the United States, ____l____ is easy. But farming has always been ____2____ in the northeastern corner of the country, ____3____ is called New England.
New England has many trees and thin, rocky ____4____. Anyone who has wanted to start a new ____5____ has had to work very hard. The first job has been cutting down trees. The ____6____ job has been digging the stumps（树桩）of the trees ____7____ the soil. Then the farmer has had the difficult job of ___8____ stones from his land.
This work of removing stones never really ____9____, because every winter more stones appear. They come up through the ____10____ soil from the rocks below. Farmers have to ___11____ removing stones from the fields. Even today, farms which have been worked on for 200 years keep ____12____ more stones.
That is why stone walls are used ____13____ fences around New England fields. The stone walls are not high; a man can easily ____14____. But they keep the farmer's cows ___15____his neighbor's cows.
D. boards