Simplify $\frac{35 y^{2}(x-3)(x+3)}{21 y(x-3)}$. (A) $\frac{5(x+3)}{3 y}$ (B) $\frac{5(x-3)}{3}$ (C) $\frac{5 y(x+3)}{3}$ (D) $\frac{5 y(x-3)}{3 y}$

Step 1 ：Rewrite the expression as \(\frac{7*5 y*y(x-3)(x+3)}{7*3 y(x-3)}\).

Step 2 ：Cancel out the common factors $7$, $y$, and $(x-3)$ to get \(\frac{5 y(x+3)}{3}\).

Step 3 ：\(\boxed{\frac{5 y(x+3)}{3}}\) is the simplified form of the given expression.

Step 4 ：Check the result by substituting any value for $x$ and $y$ into the original expression and the simplified expression. If they yield the same result, then the simplification is correct.