Put the verb in the correct form. Put the answers only

Put the verb in the correct form. Put the answers only in full forms with one space between them!
The Benton Horde, a priceless collection of ancient Roman silver, 14. _______________ (disappear) from its display cabinet in the British Museum. At todays emergency press conference, the Museum director John Clive said, that according to his theory, the treasures 15. ____________________ (probably/steal) by a professional gang on behalf of a specific collector. The matter is that the stolen silver 16. _______________ (be) very well-known and it 17. ____________________ (never/sell) on the open market.
Ten museums 18. _______________ (rob) in the last six months and the number 19. ________ (rise) steadily over the last few years. The Benton Horde 20. _______________ (consider) one of Britains most important collections of Roman silver. It 21. _______________ (lie) undiscovered for almost sixteen centuries beneath a Sussex field until it 22. _______________ (find) incidentally in 1926.