1. Historians have long been puzzled by dots, lines and symbols which have been engraved on walls, bones, and the ivory tusks of mammoths.
    长期以来，历史学家一直对雕刻在墙壁上、骨头上、古代长毛象的象牙上的点、线和形形色色的符号感到困惑不解。

2. Is it made of ivory?
    它是象牙做的吗?