ANSWER
[tex] |BC| = \sqrt{58} [/tex]
EXPLANATION
Since the given triangle has a right angle, we can apply the Pythagorean Theorem to obtain,
[tex] { |BC| }^{2} = { |AC| }^{2} + { |AB| }^{2} [/tex]
We substitute the length of the given sides to obtain,
[tex] { |BC| }^{2} = { 7}^{2} + { 3 }^{2} [/tex]
We evaluate to obtain,
[tex] { |BC| }^{2} = 49 + 9[/tex]
We simplify the right hand side to get,
[tex] { |BC| }^{2} = 58[/tex]
We take the positive square root of both sides to get,
[tex] |BC| = \sqrt{58} [/tex]
The correct answer is D.