The question asks for the correct sequence in decreasing order of the given Roman numerals. The Roman numeral system uses symbols, in this case, C, D, L, and M, to denote certain values. The value of C is 100, D is 500, L is 50, and M is 1000.

Option 1 suggests that C (100) is greater than D (500), which is incorrect, hence this sequence is wrong.

Option 2 suggests the sequence M>L>D>C, which is the correct order for M, D, and C, but L is incorrectly placed. L stands for 50, which is the smallest among the given numerals, so it should be at the end.

Option 3 presents the sequence M>D>C>L, correctly starting with M (1000) and ending with L (50), the numerals in between, D (500) and C (100), are also in correct descending order according to their values.

Option 4 indicates L as the highest value, which is incorrect as L represents 50, the smallest value among the others. Therefore, this sequence is also incorrect.

So, it is evident that answer 3 is indeed correct.