The complete solution of the linear differential equation
$$\frac{\text{d}^2z}{\text{d}t^2} + (p + q) \frac{\text{d}z}{\text{d}t} + pqz = 0$$

A

$$c_1 e^{− pt} + c_2 e^{− qt}$$

B

$$c_1 e^{pt} - c_2 e^{qt}$$

C

$$c_1 e^{− pt} + c_2 e^{qt}$$

D

$$c_1 e^{pt} + c_2 e^{qt}$$