Factor, Using the Given Factor $x ^ { 4 / 7 } + 3 x ^ { 2 / 7 } ; \quad x ^ { 2 / 7 }$

Factor, using the given factor. Assume all variables represent positive real numbers.
- $x ^ { 4 / 7 } + 3 x ^ { 2 / 7 } ; \quad x ^ { 2 / 7 }$

A) $x ^ { 2 / 7 } \left( x ^ { 2 / 7 } + 3 \right)$
B) $x ^ { 1 / 7 } \left( x ^ { 2 / 7 } + 3 \right)$
C) $x ^ { 2 / 7 } \left( x ^ { - 2 / 7 } + 3 \right)$
D) $x ^ { 1 / 7 } \left( x ^ { 4 / 7 } + 3 \right)$