Let $a _ { 1 } < a _ { 2 } < a _ { 3 } < a _ { 4 }$ be positive integers such that $$\sum _ { i = 1 } ^ { 4 } \frac { 1 } { a _ { i } } = \frac { 11 } { 6 }$$ Then, $a _ { 4 } - a _ { 2 }$ equals\\ (A) 11\\ (B) 10\\ (C) 9\\ (D) 8 .