What did you write the ANSWER as?
The symbols are as follows:
1=I, 5=V, 10=X, 50=L,100=C, 500=D, 1000=M
So,
If you repeat I(1) it becomes 2 or 3 and there is no replacement for that. So it can be repeated.
If you repeat V(5) it could become 10 or any number in 5's table, and there are Roman Numerals to replace that. For example, VVVVVVV can be replaced by XXXV. Hence, V cannot be repeated.
Then, if you repeat X(10) it can become 20 or 30 and there is no replacement for that. So it can be repeated.
Therefore, the answer is B) V.
Thank You