(Reuters) - The search for missing Malaysia Airlines Flight MH370 is likely to drag on for years, a senior U.S. defense  official told Reuters on Friday, as an underwater search for any trace of the plane off west Australia appeared to have failed.
The official, speaking under condition of anonymity（匿名）because he was not authorized to comment on the search effort, said two weeks of searching the Indian Ocean floor with a U.S. Navy had turned up no wreckage（残骸）．
He said the search for the plane, which disappeared on March 8 with 239 people on board, would now enter a much harder phase of searching broader areas of the ocean near where the plane is believed to have crashed.
”We went all-in on this small area and didn't find anything.  Now you’re got to go back to the big area," the official said.  "And now you're talking years.”
On Friday, the undersea drone. Bluefin-21 is expected to finish what may be the last of its 16-hour trips to depths of  more than 4.5 km (2. 8 miles) searching a 10 square km (6.2 square mile) area of the seabed about 2,000 miles northwest of Perth.
Authorities had identified the area as their strongest lead in determining the plane's final resting place after detecting what they suspected was a signal from the plane's black box recorder on April 4.
But the U. S.  official said Malaysia would have to decide how to continue the search, including whether to bring in more underwater drones,  even with the understanding that the search could continue for years without a refined (精确的) search area.
What does the passage mainly talk about?  ( no more than, 12 words)
                                                                            
Where did the recent search for the plane take place? ( no more than, 3 words)
                                                                            
Why didn't the official want others to know his name? ( no more than 11 words)
                                                                            
What led people to determine the plane's final resting place? ( no more than 9 words)
                                                                            
According to the passage, which country is in charge of the arrangement of the search? (1 word)