Answer:
d. Arduous.
Step-by-step explanation:
The word "laborious" means someone who is active, hardworking, persistent. It signifies someone who does grueling, difficult, wearisome work.
The given sentence is "In the arts, as in any field of endeavor, the laurels usually go to those who are as laborious as they are naturally gifted."
Here, the speaker says that the laurels usually go to those who work hard as well as are naturally gifted. But the main point is the perseverance, the 'striving for success' people. In other words, 'hardworking' also means arduous.
Thus, the correct answer is option d.