What should be the main basis for the classification of organisms?

Correct answer: Structural similarities and differences among organisms

Correct answer: B. A useful biological classification groups organisms by significant similarities and differences, especially features that reveal their structure and relationships. Scientists may study external form, internal anatomy and other biological characters; the exact evidence used can become more comprehensive as classification systems develop. Colour and size alone, as in A, can be misleading because unrelated organisms may look alike and members of one group may vary. C is wrong because commercial usefulness says nothing reliable about natural biological relationships. D is wrong because organisms living in the same region are not necessarily closely related, and related organisms may live in different regions. Classification is therefore not an arbitrary arrangement based on human benefit or location. Memory cue: classify by biological characters and relationships, not by appearance alone, usefulness or place.