Correct

百思不解

/ bǎi sī bùjiě /
Strokes

Definition

to remain puzzled after pondering over sth a hundred times (idiom)/to remain perplexed despite much thought

Example

Definition

be still unable to solve a problem after long pondering; remain perplexed despite much thought

1
gěi
huíxìn
回信
líng
bǎijiě
百思不解
  

I am puzzled by his failure to reply/that he hasn't replied to my letter.

2
Zhè
jiàn
shì
bǎijiě
百思不解
  

The answer still escapes me though I have cudgelled my brains over it.

3
Ràng
rén
bǎijiě
百思不解

beyond all comprehension