Correct

难于

/ nán yú /
Strokes

Definition

difficult

Example

As an Adverb

hard/difficult to do sth

1
Nán
难于
zòuxiào
奏效

be hard to get result

2
Nán
难于
chǐ
启齿

too shy to speak out; too embarrassed to mention

As an Adverb

harder than; more difficult than

3
Shǔdào
蜀道
zhī
nán
  
,
nánshàngqīngtiān
难于上青天
  

The road to Sichuan is as difficult as climbing to heaven.

4
第一
nán
难于
èr
第二
  

The first question is more difficult than the second.