(3)→ The number of students remaining to solve the first problem is x- 1.
→ The number of students who solved the first problem is x+(x- 1)=2x- 1 (5).
(5)+( 1)→ All students who have not solved the first question are 25-(2x- 1)=26-2x people (6).
(4)→ Number of people who only solved the second or third question = Number of people who only solved the first question =x (7)
(6)+(7)→ Among all the students who did not solve the first question, the number of students who solved the second question and the third question at the same time was 26-2x-x=26-3x (8).
(8)+(2)→ Among all the students who have not solved the first question, the number of students who have solved the second question is
(26-2x+26-3x)* 2/3 =( 104- 10x)/3； Among all the students who have not solved the first problem, the number of students who have solved the third problem is (26-2x+26-3x)/3=(52-5x)/3 (9).
(6)+(9)→ Students who have not solved the first question or the third question (that is, students who have only solved the second question) are
(26-2x)-(52-5x)/3 =(26-x)/3( 10)
The values in (5) to (9) are all greater than 0 and less than or equal to 25.
3≤x≤8
The number of students who only solve the second problem is not more than that who only solve the second or third problem.
That is, (26-x)/3 ≤ x.
So x≥7
So x=7 or 8.
In addition, both values in (9) are integers.
So x=8.
So the number of students who only solved the second problem is (26-x)/3=6 (people).
So choose B.