The correct option is D Gram $$+$$ve and Gram $$-$$ve There are various ways in which bacteria are classified based on on the basis of shape, cell wall, flagella, nutrition and morphology. The bacteria are classfied on the basis of staining as gram positive and gram negative bacteria. Gram positive bacteria retains the gram stain and appears violate under microscope after gram staining. Example includes Streptococcus aureus. Gram negative bacteria does not retain the gram stain and they take up the red colour of the counter stain in gram staining process. For example, Escherichia coli.
Thus, the correct answer is ' Gram +ve and Gram −ve.'