(1) 时态概述    英语动词的时态是指谓语动词用来表示动作、状态发生、存在的各种形式，或者表示某一动作发生或状态存在的时间和方式。英语中的动词共有16种时态。在本书以下的几个单元中，将介绍常用的12种时态。以实意动词 work 为例，其16种时态的列表如下：   方式\时间 现在 过去 将来 过去将来 一般 work/works worked shall/will work should/would work 进行 am/is/are working was/were working shall/will be working should/would be working 完成 have/has worked had worked shall/will have worked should/would have worked 完成进行 have/has been working had been working shall/will have been working should/would have been working