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