Step 1: Concept A general equation $x^2/A + y^2/B = 1$ represents a hyperbola if the signs of $A$ and $B$ are opposite.
Step 2: Meaning The product of denominators must be negative: $(7-k)(5-k) < 0$.
Step 3: Analysis This inequality holds when $k$ lies between the roots of the expression.
Step 4: Conclusion The roots are $k=5$ and $k=7$. Thus, the condition is $5 < k < 7$.
Final Answer: (A)