6542. The problem is tedious to tackle.

✅ The correct answer is option C.
Easy : achieved without great effort; presenting few difficulties.

Difficult : needing much effort or skill to accomplish, deal with, or understand.

Tiring : causing one to need rest or sleep; fatiguing.

Troublesome : causing difficulty or annoyance.

Tedious : too long, slow, or dull; tiresome or monotonous.

Synonym of Tedious is Tiring