
Option: C is the correct answer.
          C.   5
We will solve the following problem with the help of the Venn diagram.
Based on the Venn diagram we are asked to find the value of v i.e. those who have parakeet only.
From the information that:
     x+y+10=35
       i.e.
        x+y=25
Also, based on the information :
         u+z+10=28
          i.e.
         u+z=18
Also, 42 had neither a cat nor a dog nor a parakeet.
 This means it cover the outer region of the three circles.
Total 100 families were surveyed it means that:
    42+x+y+10+u+z+v=100
i.e. Â Â Â 42+25+10+18+v=100
i.e. Â Â Â Â 95+v=100
i.e. Â Â Â Â Â v=100-95
i.e. Â Â Â Â Â v=5 Â Â
Hence, the number of families who have only parakeet are: Â 5