the house built of _______was once used as a warehouse

问题描述:

the house built of _______was once used as a warehouse
答案stone
为嘛不用stones

石头的意思时,可数的
She stepped on a loose stone and twisted her ankle.
她踩到一块松动的石头上,扭伤了脚踝.
石材的意思时,是不可数的
The house is made of stone,not concrete.
那房子是石造的,不是混凝土造的