Scientists say such cycles have been an enduring - and hotly debated - mystery in ecology.

Why the city, the subways in particular, cannot tolerate more rain than usual remains an enduring mystery.

Ms. Pagan's ability to rebound has been an enduring mystery in the district.

What is in those pages is one of the enduring mysteries in the investigation.

How Asia made that transition may prove to be one of the most enduring economic mysteries of the 1980's.

Why they stoop to accept something free, considering how much money they make, is an enduring mystery.

But what happened in the dark age and how the light came on again is an enduring and frustrating mystery.

That such concerns so often block economically efficient programs is one of the enduring mysteries of modern political economy.

She had been beaten to death with a golf club under a weeping willow in what has become an enduring mystery.

The timing and manner of his death is a matter of some enduring mystery.