The correct answer is:
Bacillus is a diversity of gram-positive, rod-shaped bacteria and a member of the phylum Firmicutes. Bacillus species can be obligate aerobes or facultative anaerobes. Many species of Bacillus can generate extensive quantities of enzymes which are applied in various industries.
Coccis are more spherical
Staphus a living formation
Spirillum is a long strand
Round bacteria is called cocci (singular: coccus), cylindrical, capsule-shaped ones known as bacilli (singular: bacillus); comma shaped called vibro(eg: vibro cholerae) and spiral bacteria, aptly called spirilla (singular: spirillum).
Hope it helps.
it would most likely be C.) bacillus