The phrase "a challenge has been" is correct and usable in written English.
It can be used when discussing a challenge that has occurred or been presented in the past.
Example: "A challenge has been identified in the project that requires immediate attention from the team."
Alternatives: "a challenge was posed" or "a challenge has arisen".
A challenge has been laid down.
Today a challenge has been posed to all of us.
Pienaar, never one to shirk a challenge, has been cautioned in two of his last three starts and, at 14-1 (Blue Square), is a fair wager.
A cracked fingertip amid such a challenge has been compared to a blown tire in the final stage of the Tour de France.
A challenge has been to keep our best players in England: some of them are in big demand across the water and it is hard to compete with some of the money on offer, which is why the policy of picking players for the national side if they play in the Premiership is so important.
For Paramount, a challenge has been to keep guerrillas like Mr. Blum and Mr. Peli, whose "found footage" films cost a few million dollars, at most, from colliding with gorillas like Mr. Abrams and Mr. Spielberg, who are spending about $50 million on "Super 8," an effects-filled movie that is supposed to deliver the energy, but not the shaky production values, of the amateur camera.
But this time the trials, rather than a challenge, have been breathtakingly cruel.
Previously, the process of reviewing a decision only began after a challenge had been issued.
A major challenge has been a sharp reversal in video game sales.
A similar challenge has been documented in a previous study on the copy number variation of nuclear MITEs (miniature inverted-repeat transposable elements) (Fattash et al. 2013).
Within the field of cell signaling, a great challenge has been to distinguish between competing signaling pathways within a cell.
