The correct answer is MMX. In Roman numerals, M stands for 1000, so two Ms give 2000, and X stands for 10, so MMX equals 2000 plus 10, which is 2010. Roman numerals build numbers by adding the values of letters written in decreasing order from left to right, and this is exactly how MMX is formed.
The other options are not valid Roman numeral constructions or represent different values. LLX is not a standard way to write numerals since L, which stands for 50, is never repeated in proper Roman numeral notation. IIXX and CCXX also break the standard rules, since I and X can only be repeated up to three times in a row and cannot be combined the way shown here to legitimately reach 2010.
Roman numeral basics worth remembering are I equals 1, V equals 5, X equals 10, L equals 50, C equals 100, D equals 500 and M equals 1000, and only M, C, and X style symbols are meant to be repeated, never L, V or D.