Which one of the following is a separable first-order differential equation? A. t² dx/dt - t² x² = 7t³ x² − 18t⁷x² + 7x B. xt dx/dt - t²x² = 7t³ x² − 18t⁴x² + 7x C. x² dx/dt - t²x² = 7t³x² - 18t⁷ x² + 7x²
D. dx/dt - t²x² =18t⁴x² - 7t³x² + t²x² - 7x
O D
O A
O C
O B