Synonym of ONEROUS

Answer: Option C

Difficult : needing much effort or skill to accomplish, deal with, or understand.
Awesome ; extremely impressive or daunting; inspiring awe.
Burdensome : difficult to carry out or fulfil; taxing.
Dutiful : conscientiously or obediently fulfilling one's duty.
Onerous : (of a task or responsibility) involving a great deal of effort, trouble, or difficulty.

Synonym of Onerous is Burdensome