Correct Option: D

C(s)	=	K.(1/s3 + 3s2 + 2s + 1)
R(s)		1 + (1/s3 + 3s2 + 2s + 1)× 1

and C.E = 1 + G(s) H(s)

⇒ + 1	K	. 1 = 0
	s3 + 3s2 + 2s + 1

⇒ s³ + 3s² + 2s + 1 K = 0
The Hurwitz criterion can be given as
s³ 1 2
s² 3 1 + K
s³ 6 – (1 + K)/3 0
s⁰ 1 + K 0
for the system to be stable

6 – (1 + K)	≥ 0
3

and
1 + K ≥ 0
6 ≥ 1 + K
or
1 + K ≤ 6
or
K ≤ 5
K_max = 5