Answer:
<u>Option D. 21</u>
Step-by-step explanation:
The question is as shown in the attached figure 1
The Venn diagram representing the problem is the attached figure 2
D ⇒ Dog , C⇒ Cat  and P ⇒ parakeet
Let the The families had parakeet only = X
A survey of 260 families show that:
 99 had dog 
76 had cat 
34 had dog and cat 
98 had neither a cat nor a dog nor a parakeet 
8 had a cat a dog and a parakeet
So, 
The families had a dog and a cat only = 34 - 8 = 26
The families had a dog only = 99 - (26 + 8 ) = 65
The families had a cat only = 76 - (26 + 8) = 42
∴ X = 260 - ( 98 + 8 + 26 + 65 + 42 ) = 260 - 239 = 21
So, The families had a parakeet only = 21
<u>The answer is option D</u>