What physical features would a traveler oh the Silk Road likely not have encountered? * (A )desert (B)mountain(C) tundra (D)rivers​

You have been tasked with sorting the rock samples shown into three categories, with two rocks in each category. what attribute would you use to sort these rocks? which rocks would be in each category? rocks: obsidian, coquina limestone, granite, soapstone,pumice, and gneiss.