A pair of fair 6 -sided dice is rolled $n$ times. What is the least value of $n$ such that the probability that the sum of the numbers face up on a roll equals 7 at least once is greater than $\frac{1}{2}$ ? 
选项为:A:$$2$$  B:$$3$$  C:$$4$$  D:$$5$$  E:$$6$$  请回答其中一个选项.