Which of the following numbers has the largest prime factor?
$\text{(A)}\ 39\qquad\text{(B)}\ 51\qquad\text{(C)}\ 77\qquad\text{(D)}\ 91\qquad\text{(E)}\ 121$
A. The prime factors of $39$ are $3$ and $13$. Therefore, the largest prime factor is $13$.
B. The prime factors of $51$ are $3$ and $17$. Therefore, the largest prime factor is $17$.
C. The prime factor of $77$ are $7$ and $11$. Therefore, the largest prime factor is $11$.
D. The prime factor of $91$ are $7$ and $13$. Therefore, the largest prime factor is $13$.
E. The prime factor of $121$ are $11$. Therefore, the largest prime factor is $11$.
So, the answer is $B$