back背部是物质名词还是抽象名词或其他?

问题描述:

back背部是物质名词还是抽象名词或其他?

back 是名词,副词,形容词和动词.
作为名词,back 既是物质名词,也是抽象名词.请看例句:
Honey can you scratch my back please? It is very itchy. (back 是物质名词)
At the back of my mind is this constant fear of failure. (back 是抽象名词)