Correct
殚精竭虑
/ dān jīng jié lǜ /
Strokes
Definition
to exhaust one's thoughts and ingenuity (idiom); to think sth through thoroughly/to rack one's brains/to leave no stone unturned
Example
Definition
beat/cudgel/rack one's brains; tax one's ingenuity; devote one's entire energy and thought (to)