What is the unit step response of the system described by the difference equation?

[answerhappygod]

y(n)=0.9y(n-1)-0.81y(n-2)+x(n) under the initial conditions y(-1)=y(-2)=0?
a) [1.099+1.088(0.9)n.\(cos(\frac{\pi}{3} n+5.2^o)\)]u(n)
b) [1.099+1.088(0.9)n.\(cos(\frac{\pi}{3} n-5.2^o)\)]u(n)
c) [1.099+1.088(0.9)n.\(cos(\frac{\pi}{3} n-5.2^o)\)]
d) None of the mentioned