Question

Three capacitors are connected in series across a
DC power source that produces a constant potential
difference. A fourth capacitor is now added in series with
the other three. As a result of adding this capacitor, the
total energy stored in the system of capacitors has

B. decreased.

Can someone explain to me how the total system of capacitors has decreased energy?

So if I add another capacitor in series it decreases the capacitance further. But I dont understand what it does to charge and voltage.