D. Increase income, interest rates remain unchanged

First of all, due to the existence of the liquidity trap in the Keynesian region, the LM curve is close to the horizontal line, so the rightward shift of the IS curve will only make the Income Y increases without increasing interest rates i.

Secondly, investment is neither a fiscal policy nor a monetary policy. It is an act of the private sector. However, increased investment and expansionary fiscal policy will shift the IS curve to the right.

Hope it helps.