他们已经工作两个小时了.They have been working for two hours.They have worked for two hours.哪个

题目

他们已经工作两个小时了.They have been working for two hours.They have worked for two hours.哪个
他们已经工作两个小时了.
They have been working for two hours.
They have worked for two hours.
哪个对,两个句子有何区别.

答案

They have been working for two hours.
现在完成进行时.
表示截止现在,他们已经工作2小时（并仍在继续工作）.
They have worked for two hours.
现在完成时.
表示他们已经工作了2小时,但不见得仍在继续工作.