Seven persons — A, B, C, D, E, F and G — are attending an event one after another, but not necessarily in the same order.
G attends the event three persons after C. B attends the event immediately before C. Only one person attends the event between B and E. D attends the event four persons after E but before A. Three persons attend event between A and F.

How many persons attend between B and A?

The correct option is Two.

Let us step-by-step determine the order of the seven persons (positions 1 through 7) attending the event based on the given clues:

Step 1: Analyze the relative positions of C, G, B, and E.
1. "G attends the event three persons after C."
This means if C is at position x, G is at position $x+3$.
So, the arrangement has C _ _ G.

2. "B attends the event immediately before C."
So, B is right before C. The block becomes B C _ _ G.

3. "Only one person attends the event between B and E."
Since B C _ _ G has C immediately after B, E cannot be placed after B (because position after C is occupied or creates conflict). Thus, E must attend before B with one person between them.
So, the block expands to: E _ B C _ _ G.

Step 2: Determine the exact positions for the 7 persons.
The block "E _ B C _ _ G" consists of exactly 7 positions in sequence!
Let us assign the positions 1 to 7:
1: E
2: _
3: B
4: C
5: _
6: _
7: G

Step 3: Place D, A, and F in the remaining positions.
1. "D attends the event four persons after E but before A."
Since E is at position 1, four persons after E means position $1+4=5$.
So, D is at position 5.

Also, D attends before A. The remaining empty positions are 2 and 6. Since D is at position 5 and attends before A, A must be at position 6.

2. Now, position 2 is the only remaining empty spot, so F must be at position 2.

3. "Three persons attend event between A and F."
Let us verify: F is at position 2 and A is at position 6. The persons at positions 3, 4, and 5 (B, C, D) are between F and A. Exactly three persons! This confirms our arrangement.

Final Arrangement:
1. E
2. F
3. B
4. C
5. D
6. A
7. G

Answering the question:
We need to find how many persons attend between B (position 3) and A (position 6).
The persons attending between B and A are C (position 4) and D (position 5).
Therefore, exactly Two persons attend between B and A.