Statement:
All stones are hammers. No hammer is a ring. Some rings are doors.
All doors are windows.
Conclusions:
I. Some windows are stones.
II. Some windows are rings.
III. No window is a stone.
IV. Some rings are stones.

Some rings are doors + All doors are windows = I + A = I = Some rings are windows ? Conversion ? Some windows are rings(I) Hence II follows. All stones are hammers + No hammer is a ring = A + E = E No stones is a ring ? conversion ? No ring is a stone (E) Hence IV does not follows. No stone is a ring + Some rings are doors = E + I = O* = Some windows are not stones Hence either I or II follows as they form a complementary I-E pair.