Question

a blue whale lives in water, bat can fly and man can walk on two feets, still these animals are grouped together. name the group and state the basis of their grouping by giving 4 points

Answer 1

They all belongs to 

Kingdom - Animalia
Phylum - Vertebrata 
Class - Mammalia 

They have mammary glands to nourish their young ones. Sweat gland and oil glands are present in them.They are warm blooded animals and have 4 chambered heart.

Answer 2

they all are grouped under Vertebrtes
  the main features are:they r bi laterally symmetrical
                                      they have true vertibral column
                                      they have dorsal nerve chord
                                       triploblastic
                                       coelomate
                                         internal skeleton