Root Locus, Transfer Functions and Unit Step Response?
The closed loop poles are the roots of the polynomial
$$D(s)=s^2+2s+2+K\tag{1}$$
and, according to the root locus plot, they are $s_{1,2}=-1\pm 2j$. Consequently, we get
$$2+K=|1+2j|^2=5\quad\Longrightarrow\quad K=3\tag{2}$$
With $K=3$ we obtain $$H(0)=\frac{K}{2+K}=\frac35\tag{3}$$
which leaves step response $C$ as the only option.