Scientists have been trying to solve the difficult problem for centuries.
難易度：高（11語）
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He has been waiting for his girlfriend for hours.
She thought that her brother was watching TV.
They have been looking for an apartment for months.
I hope that you will come again.
Nancy has been working here for ten years.
She believes that he will come back some day.
That boy has been running for over an hour.
Do you know that he came here yesterday?
I have been reading this book for two hours.
I think that she lives in America.
She has been playing the piano for more than three hours.
They did not know(that) they were wrong.