Complex sentence: Until 2007 none of the Dornier twin-engined bomber variants were thought to have survived intact, but various large relics of the Do 17 and Do 215 are held by public museums and private collectors.
Split into simpler sentences: Until 2007 none of the Dornier twin-engined bomber variants were thought to have survived. Various large relics of the Do 17 and Do 215 are held by public museums and private collectors.