The gates $G_{1}$ and $G_{2}$ in the figure is have propagation delays of $10 \; \mathrm{nsec}$ and $20 \; \mathrm{nsec}$ respectively. If the input $\mathrm{V}_{\mathrm{i}}$ makes an abrupt change from logic $0$ to $1$ at time $t=t_{0}$, then the output wave form $V_{0}$ is.
