Ans. is 'a' i.e., Listeria o Information in this question areGram positiveCocobacilliTumbling motilityo Listeria is gram positive coccobacilli and shows characteristic tumbiling motility when grown at 25degC.o Other options can easily be excludes as no one has tumbling motility (charactristic of Listeria) and no one is gram- positive coccobacillusi)Meningococci: Gram-negative cocciii) H. influenza: Gram-negative bacilliiii) Pneumococcus: Gram-positive cocci