The differential equation model for two first-order systems in series is x(t)+ 4x(t)+ 3x(t) = u(t), where u(t) is the input of the first system and x(t) is the output of the second system. The response x(t) of the system to a unit impulse u(t) is:

a. x(t)=e-2e-21 1 b. x(t)= -21 = - 1 -31 -e 3 CG x(1)=-10-31 c. 2 2 d. x(t)=e-e-31 e