Correct

敲门砖

/ qiāoménzhuān / 
Strokes

Definition

lit. a brick as a door knocker (idiom); fig. a temporary expedient/to use sb as a stepping stone to fortune

Example

As a Noun

brick picked up to knock on the door and thrown away when it has served its purpose―stepping-stone to success

1
Yǒurén
有人
bǎ
把
shàngxué
上学
dàngchéng
当成
qiāoménzhuān
敲门砖
  
,
yīdàn
一旦
gōngmíng
功名
dàoshǒu
到手
  
,
shūjí
书籍
yě
也
jiù
就
bèi
被
shùzhīgāogé
束之高阁
le
了
  
。

Some people take attending school only as a stepping-stone to status; once they succeed, all the books will be shelved.