1.   A pain attack could happen any time, and Thompson tries to sense when internal malfunctions are brewing.

2.   Others have said the explosion could have been caused by a World War II-era mine or an internal malfunction.

3.   Airline officials said it was impossible for the plane to explode from an internal malfunction since the engines had not yet been started.

4.   Airline officials said it was unlikely the plane would have exploded from an internal malfunction if the engines had not yet been started.

5.   Airline officials said it was unlikely the plane could have exploded from an internal malfunction if the engines had not yet been started.

6.   Airline officials said it was unlikely the plane could have exploded from an internal malfunction since the engines had not yet been started.

7.   Airline officials said it was unlikely the plane could have exploded from an internal malfunction if the engines had not been started.

8.   An internal malfunction, a collision with a World War II mine or a collision with a foreign submarine are likely causes, they said.

9.   Authorities have theorized about a collision with a Western submarine or a World War II-era mine or an internal malfunction as possible reasons.

10.   Many Russian officials have said it was likely a collision with a foreign vessel, but other observers say an internal malfunction was the most likely explanation.