The signal flow graph of a system is shown below. $U(s)$ is the input and $C(s)$ is the output.

Assuming, $h_1=b_1$ and $h_0=b_0-b_1a_1$ , the input-output transfer function, $G(s)=\frac{C(s)}{U(s)}$  of the system is given by

1. $G(s)=\frac{b_0s+b_1}{s^2+a_0s+a_1} \\$
2. $G(s)=\frac{a_1s+a_0}{s^2+b_1s+b_0} \\$
3. $G(s)=\frac{b_1s+b_0}{s^2+a_1s+a_0} \\$
4. $G(s)=\frac{a_0s+a1}{s^2+b_0s+b_1}$

edited