HSK 5
Correct

后背

/ hòubèi / 
Strokes

Definition

the back (human anatomy)/the back part of sth

Example

As a Noun

back (of the human body)

1
Pāi
拍
hòubèi
后背

pat sb on the back

2
Cuō
搓
hòubèi
后背

rub one's back

As a Noun

rear; behind

3
Gōngjī
攻击
dírén
敌人
hòubèi
后背

attack the enemy from behind