Find the correct output

Question

Answer 1

at t<t0
output of NOR gate is 1. and input Vi is 1 so input to Ex-or gate is 1,0 ..
final output ll be 1..

at t0<t<t1
input to NOR gate is 1 but still output or NOR gate is 1 (due to propagation delay). Input to Ex-OR gate is 1,1 and final output ll b 0..

at t1<t<t3
input to NOR gate is 1 and here output of NOR gate is 0.
 Input to Ex-OR gate is 0,1 but fiinal output ll b 0 (due to propagation delay of Ex- OR gate)..

at t>t3.
input to NOR gate is 1 and here output of NOR gate is 0.
Input to Ex-OR gate is 0,1 and  fiinal output ll b 1..
 
Option A..
m assuming difference between two consecutive ti (i=0 to3) value is 10nsec..

Comments

I think it should be B

In time to < t < t1 you are not considering that output of exor gate will be out after 20ns.