HSK C7-9
Correct

呜

/ wū / 
Strokes

Definition

(onom.) for humming or whimpering

Example

As an Onomatope

toot; hoot; zoom

1
Huǒchē
火车
wū
呜
dì
地
fēichí
飞驰
ér
而
guò
过
  
。

The train tooted/zoomed past.

2
Hè
吓
de
得
wūwū
呜呜
kū
哭
qǐlai
起来

begin to whimper with fear

3
Wūwū
呜呜
de
地
kū
哭
gè
个
méiwán
没完

sob away uncontrollably