Answer: C
\(\cfrac{3\sqrt{8} - 2\sqrt{12} + \sqrt{20}}{3\sqrt{18} - 2\sqrt{27} + \sqrt{45}}\) \(= \cfrac{3 \times 2\sqrt{2} - 2 \times 2\sqrt{3} + 2\sqrt{5}}{3 \times 3\sqrt{2} - 2 \times 3\sqrt{3} + 3\sqrt{5}} \) \(= \cfrac{6\sqrt{2} - 4\sqrt{3} + 2\sqrt{5}}{9\sqrt{2} - 6\sqrt{3} + 3\sqrt{5}} \) \(= \cfrac{2(3\sqrt{2} - 2\sqrt{3} + \sqrt{5})}{3(3\sqrt{2} - 2\sqrt{3} + \sqrt{5})} \) \(= \cfrac{2}{3} \)
\(\cfrac{3\sqrt{8} - 2\sqrt{12} + \sqrt{20}}{3\sqrt{18} - 2\sqrt{27} + \sqrt{45}}\) \(= \cfrac{3 \times 2\sqrt{2} - 2 \times 2\sqrt{3} + 2\sqrt{5}}{3 \times 3\sqrt{2} - 2 \times 3\sqrt{3} + 3\sqrt{5}} \) \(= \cfrac{6\sqrt{2} - 4\sqrt{3} + 2\sqrt{5}}{9\sqrt{2} - 6\sqrt{3} + 3\sqrt{5}} \) \(= \cfrac{2(3\sqrt{2} - 2\sqrt{3} + \sqrt{5})}{3(3\sqrt{2} - 2\sqrt{3} + \sqrt{5})} \) \(= \cfrac{2}{3} \)