Find the Vo at Vs = 10V?
D1: is off (cathode +10V, no way to get 0.7V from A to C)

D2: assuming D4 is off, 10V across the branch --> Diode is on, will result in 0.7V across the diode the rest will drop across the two 10k resistors. (9.3V / 2 = 4.65V across each resistor)

D3: is on, C 0.7V below the input at 9.3V

D4: Output is at 4.65V, C is at 9.3V --> Diode is off (assumption was OK)