wall bookcase的用法和樣例：
例句
- He hid his hard-earned two thousand yuan cash inside a double wall in his apartment.
他把辛苦得來的二千元現款藏在住處的夾層牆裡。 - One large compartment of the aviary served as the caching arena.We separated a smaller compartment from this area with an opaque wall.
我們將大鳥籠里的一個大空間，當渡鴉的藏寶區，再以不透明的牆隔出一較小的區域，其中有隔間。
