Which of the following differential equations has y = c1 ex + c2 e-x as the general solution? $(A)\frac{{{\partial }^{2}}y}{\partial {{x}^{2}}}+y=0(B)\frac{{{\partial }^{2}}y}{\partial {{x}^{2}}}-y=0(C)\frac{{{\partial }^{2}}y}{\partial {{x}^{2}}}+1=0(D)\frac{{{\partial }^{2}}y}{\partial {{x}^{2}}}-1=0$.