Two Zener diodes (A and B) having breakdown voltages of

Two Zener diodes (A and B) having breakdown voltages of $6 \mathrm{~V}$ and $4 \mathrm{~V}$ respectively, are connected as shown in athe circuit below. The output voltage $V_{0}$ variation with input voltage linearly increasing with time, is given by :

$\left(V_{\text {input }}=0 \mathrm{~V}\right.$ at $\mathrm{t}=0$ ) (figures are qualitative)