When autonomous investment increases in a two-sector model, then.

1. The aggregate demand curve shifts upwards.
2. Output/GDP increases by the same magnitude as the change in investment.
3. Autonomous expenditure increases by the same magnitude as the change in investment.
4. The consumption curve shifts upwards.

Option 1 -> When autonomous investment increases, the investment component of aggregate demand rises, causing the entire AD curve to shift upward.

Option 2 -> Due to the multiplier effect, output increases by MORE than the change in investment (ΔY = k × ΔI, where k > 1).

Option 3 -> While technically true by definition, this is merely an accounting identity rather than an economic consequence.

Option 4 -> The consumption function itself doesn't shift; rather, higher income leads to movement along the consumption curve.

Hence, The aggregate demand curve shifts upwards -> In a two-sector model, AD = C + I. When autonomous investment (I) increases, aggregate demand increases at every income level, causing a parallel upward shift of the AD curve. This leads to a new equilibrium with higher output through the multiplier process (ΔY = k × ΔI, where k = 1/(1-MPC)). The consumption curve itself remains unchanged, but consumption increases due to the induced effect of higher income -> correct