the jewels were locked in a strong box the thieves stole them without any difficulty.A. I

问题补充：

the jewels were locked in a strong box，the thieves stole them without any difficulty.

A. If

B. Unless

C. Although

D. Because

答案：

A. If

B. Unless

(答案→)C. Although

D. Because

解析：句意：尽管珠宝被锁在一个结实的箱子里，小偷还是毫不费力地偷走了它们。故此处用Although引导让步状语从句。