【比较】
一般过去时表示的动作或状态都已成为过去，现已不复存在。
Christine was an invalid all her life.(含义：她已不在人间。)考试用书
Christine has been an invalid all her life.(含义：她现在还活着。)
Mrs. Darby lived in Kentucky for seven years.(含义：达比太太已不再住在肯塔基州。)
Mrs. Darby has lived in Kentucky for seven years.(含义：现在还住在肯塔基州，有可能指刚离去。)
注意：用过去时表现在，表示委婉语气。
1)动词want, hope, wonder, think, intend 等。
例：Did you want anything else?
I wondered if you could help me.
2)情态动词 could, would.
例：Could you lend me your bike?
