Simplify Assume All Variables Represent Nonnegative Values $\frac { \sqrt { 9 } } { \sqrt { 49 } }$

Simplify. Assume all variables represent nonnegative values.
- $\frac { \sqrt { 9 } } { \sqrt { 49 } }$

A) 21
B) $\frac{3}{7}$
C) $\frac{7}{3}$
D) 1