Let's fill the table:
1. 34+18=52;
2. 97-57=40;
3. 34+57+x+6=125,
x=125-97,
x=28;
4. 28+15=43;
5. 6+2=8;
6. 18+40+15+2=75.
Then the table is:
Let's see the options:
A. Out of the 125 children who do not have a pet, 18 of them have 2 siblings.
This option is false, because 125 children have a pet, not as in statement.
B. Out of the 97 children who have 1 pet, 40 of them do not have any siblings.
This option is false, because 97 children have 1 Sibling, not 1 pet.
C. Out of the 125 children who do not have any siblings, 34 of them have a pet.
This option is false, because 125 children have a pet, not do not have siblings.
D. Out of the 97 children who have 1 sibling, 40 of them do not have a pet.
This option is true, you can see from the table that among 97 children that have 1 Sibling, exactly 40 do not have a pet.
Answer: correct choice is D.