As per the above given question , we can say that
Chair and Table are two types of Furniture and table and chair are different from each other.
Therefore , option ( D ) gives the best relationship between Tables, Chairs and Furniture.

According to above given question , we can say that
Forests are different from Mountains.
But both are found on the Earth.
From above it is clear that option ( A ) represents the best relationship between Mountains, Forests and Earth . As shown in given venn - diagram .

According to above given question , we can say that
There are 100 students in Computer Science which include students of electronics too.
Numbers of students who study both Computer Science and Electronics = 80
? Number of students opting for Computer Science only = 100 ? 80 = 20
Therefore , 20 students study Computer Science only .

According to above given question , we can say that
Dog is different from cat.
But both may be pet.
Some dogs and cats may not be pet.
It is clear that option ( D ) represents the best relationship between DOG, CAT and PET . As shown in given venn - diagram .

According to above given question , we can say that
Pigeons come under the class Birds.
Dog is a mammal.
It is clear that option ( A ) represents the best relationship between Pigeons, Birds and Dogs. As shown in given venn - diagram .

On the basis of above given question , we know that
Parrot is a bird. Horse is an animal.
From above it is clear that option ( B ) represents the best relationship between horses, parrots and birds . As shown in given venn - diagram .

According to above given question , we can say that
Tables are different from chairs.
But both come under the class Furniture.
It is clear that option ( B ) represents the best relationship between Tables, Chairs and Furniture. As shown in given venn - diagram .

On the basis of above given question , we know that
Tiger is different from Lion.
Both are Animals.
From above it is clear that option ( C ) represents the best relationship between Tiger, Lions and Animals. As shown in given venn - diagram .

As we know that ,
Function keys are different from letter keys but both are parts of keyboard.
It is clear that option ( B ) represents the best relationship between Keyboard, function keys and letter keys. As shown in given venn - diagram .

On the basis of above given question , we can say that
All writers (C) and all pianists (B) are doctors (A).
From above it is clear that option ( B ) will be required answer .