Logic Gates question from JEE Main 2021 (26 Feb, Shift 2)

Answer: (a)

1. NAND with joined inputs gives $\bar{A}$; OR gives $\bar{A} + B$; NOT gives $Y = \overline{\bar{A} + B} = A\bar{B}$.
2. So $Y = 1$ only when $A = 1$ and $B = 0$.
3. 0–1 s: $A=1, B=0 \Rightarrow Y=1$; 1–2 s: $B=1 \Rightarrow Y=0$; 2–3 s: $A=0 \Rightarrow Y=0$; 3–4 s: $B=1 \Rightarrow Y=0$; 4–5 s: $A=1, B=0 \Rightarrow Y=1$.
4. So the answer is (a): high for 0–1 s and 4–5 s.