Correct Option: B

Steady state error, e_ss = _{s → 0} lim sE(s)
where,

E(s)	=	1
R(s)		1 + G(s) H(s)

or

E(s) =	R(s)
	1 + G(s) H(s)

ess = s → 0lim s.		R(s)
		1 + G(s) H(s)

given, r(t) = tu(t)
or
R(s) = 1/s²
Now,
(a) When,

G(s) H(s) =	30
	s2 + 6s + 9

ess =s → 0lim	1/s2 · s
	1 + {30 (s2 + 6s + 90)}

=s → 0lim	(s2 + 6s + 90)s	= ∞
	s2(s2 + 6s + 120)

(b) When,
G(s) H(s) = 30/s² + 6s

ess =s → 0lim	(1/s2)s
	1 + (30/s2 + 6s)

=s → 0lim	(s2 +6)s
	s2(s2 + 6s + 30)

= 6/30 = 0·2
(c) When,
G(s) H(s) = 30/s² + 9s

ess =s → 0lim	(1/s2)s
	1 + (30/s2 + 9s)

=s → 0lim	(s2 +9)s
	s2(s2 + 9s + 30)

= 9/30 = 0·3

G(s) H(s) =	s + 1
	s2

ess =s → 0lim	s(1/s2)	=	s	= 0
	1 + (s + 1)/s2		s2 + s +1

Hence alternative (D) is the correct choice.