词汇讲解：

1. displace vt.移动，移走; 替换，取代
例句：Yet traditions are difficult to displace. 
但传统习惯却很难改变。 

2. provide vt. 提供，供给
例句：In other words, menus provide a pedagogic vector. 
换句话说，菜单是一条学习的途径。 

3. contract n.合同; 契约
例句：A contract is invalidated if only one party signs it. 
如果只有一方签字，契约即无效。 

4. approval n.同意; 批准
例句：The deal had the tacit approval of the President. 
这笔交易得到总统的默许。  
 
5. estimate vt.估计，估算
例句：Statisticians can estimate the highest expected winds. 
统计人员能估计最大风速。
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