第二节 语法填空（共10小题; 每小题1.5分，满分15分）
阅读下面短文，按照句子结构的语法性和上下文连贯的要求，在空格处填入一个适当的词或使用括号中词语的正确形式填空，并将答案填写在答题卷标号为31-40的相应位置上。
In the 1950s, the family that owned the farm near Beulah, Michigan kept a bull chained to the elm（榆树）. The bull paced 31 the tree, dragging a heavy iron chain with him, which led to a groove（槽）in the bark. The groove 32 （deep）over the years. Though for whatever reason, it did not kill the tree.
