The block diagram of a system is illustrated in the figure shown, where $X(s)$ is the input and $Y(s)$ is the output. The transfer function $H(s)=\dfrac{Y(s)}{X(s)}$ is
1. $H(s)=\frac{s^{2}+1}{s^{3}+s^{2}+s+1}$
2. $H(s)=\frac{s^{2}+1}{s^{3}+2s^{2}+s+1}$
3. $H(s)=\frac{s+1}{s^{2}+s+1}$
4. $H(s)=\frac{s^{2}+1}{2s^{2}+1}$