Microorganism motile at 25deg C but not motile at 37deg C-
Ans. is 'a' i.e., Listeria monocytogens Listeria monocytogens exhibits characteristic, slow, tumbling motility when grown at 25degC but at 37degC it is non motile.
Listeria monocytogens
Campylobacter
Yersinia pestis
Streptococcus agalctiae