The characteristic equation of a closed loop automatic control system in time domain is given by 
$D^{5 } + 2D^{4} +4D^{2} + D + 1 = 0$ Consider the following statements in this regard
1. The system is linear
2. The system is non – linear
3. The system is stable
4. The system is unstable
(a) 1 and 3are correct
(b) 2 and 3 are correct
(c) 1 and 4 are correct
(d) 2 and 4 are correct