Correct

中空

/ zhōngkōng / 
Strokes

Definition

hollow/empty interior

Example

As an Adjective

hollow; empty inside

1
Zhè
这
kē
棵
shù
树
yǐjīng
已经
zhōng
中
kōng
空
le
了
  
。

The tree is hollow.

As a Noun

mid-air

As a Noun

medium altitude