问题1 .我在英语学习机里面看到2个关于动词cost的句子.搞不懂什么时候加s了.
1 the book costs 15 yuan (为什么加S)
2 how dear the lesson costs
3 the work cost them much labour (怎么又不加S)
4 the accident cost him his life
第一、二个因为是第三人称单数,所以加s;第三、四个是
过去式;
难道the book 和 the lesson是第三人称单数吗....第3人称不是he she it吗