二、若 (x - y)dx - xdy = 0，則其通解為 (A) x^2/2 - xy = C (B) x^2/3 - xy = C (C) x^2/3 - y = C (D) x^2/2 - y = C

五、若 \( y''' - y = 0 \)，則其通解為 (A) \( C_1 e^x + e^{\frac{1}{2}x} (C_2 \cos \sqrt{3}x + C_3 \sin \sqrt{3}x) \) (B) \( C_1 x + e^{\frac{1}{2}x} (C_2 \cos \sqrt{3}x + C_3 \sin \sqrt{3}x) \) (C) \( C_1 e^x + e^{-\frac{1}{2}x} (C_2 \cos \frac{\sqrt{3}}{2}x + C_3 \sin \frac{\sqrt{3}}{2}x) \) (D) \( C_1 x + e^{-\frac{1}{2}x} (C_2 \cos \frac{\sqrt{3}}{2}x + C_3 \sin \frac{\sqrt{3}}{2}x) \)