The correct option is D CCLX
If a Roman numeral of smaller value is placed before one with larger one, we subtract instead of adding.
CDX = 500 - 100 + 10 = 410
CL = 100 + 50 = 150
Thus, CDX - CL = 410 - 150 = 260.
But, 260 = 100 + 100 + 50 + 10 = CCLX.