Seven boxes, A, B, C, D, M, N and O, are kept one over the other but not necessarily in the same order.
No box is kept above B. Only three boxes are kept between B and N. Only one box is kept between D and A. Only C is kept below O. A is kept immediately above N. Only four boxes are kept between D and C. How many boxes are kept below M?

The correct option is Four.

Let us arrange all seven boxes from top (position 7) to bottom (position 1) step-by-step based on the given clues:

1. "No box is kept above B."
This means Box B is at the topmost position (Position 7).

2. "Only three boxes are kept between B and N."
Counting down from Position 7 (B):
- Position 6
- Position 5
- Position 4
So, Box N must be at Position 3.

3. "A is kept immediately above N."
Since Box N is at Position 3, Box A must be directly above it at Position 4.

4. "Only one box is kept between D and A."
Box A is at Position 4. Since Position 3 is occupied by N, moving downwards is not possible for a 1-box gap to D (Position 2 would be only 1 box below, but let's check upward vs downward). Moving upwards by 2 positions gives Position 6 for D.

5. "Only C is kept below O."
This means Box C is at the very bottom (Position 1), and Box O is directly above it at Position 2.

6. "Only four boxes are kept between D and C."
Since C is at Position 1, the box four positions above it (Positions 2, 3, 4, 5 in between) is at Position 6. This confirms Box D is indeed at Position 6.

7. Now, let us check the remaining unassigned box:
The remaining empty position is Position 5, which must be occupied by Box M.

The final order of boxes from top to bottom is:
Position 7: B
Position 6: D
Position 5: M
Position 4: A
Position 3: N
Position 2: O
Position 1: C

We are asked: "How many boxes are kept below M?"
Box M is at Position 5. The boxes kept below M are A, N, O, and C.

Therefore, there are exactly 4 boxes kept below M.