# Form the differential equation representing family of curves $y = A \cos (x + B)$ where A and B are parameters
$(A)\; \frac{d ^2y}{dx^2} +y=0$
$(B)\; \frac{dy}{dx} +y=0$
$(C)\; \frac{d ^2y}{dx^2} -y=0$
$(D)\; \frac{dy}{dx} +y=0$