MMX is correct. Roman numerals work by stacking values in decreasing order and adding them together. M represents 1000, and writing it twice gives 2000. X represents 10. Put them together as MMX and you get 2000 plus 10, which lands exactly on 2010.
None of the other choices follow valid Roman numeral rules. Letters like L, V, and D are never meant to be repeated more than once in a row, so an option like LLX, doubling up the L, breaks that basic rule right away. Similarly, IIXX and CCXX try to stretch I, X and C repetitions or combinations in ways that Roman numeral convention does not allow, since I and X can be repeated at most three times consecutively and even then only in specific patterns.
A quick refresher on the base symbols helps here: I is 1, V is 5, X is 10, L is 50, C is 100, D is 500, and M is 1000. Only I, X, C and M are ever repeated to build larger numbers, while V, L and D appear just once. Following these rules, the year 2010 is correctly written as MMX.