Streptococci causing dental caries :: (A) Streptococci equisimilis, (B) Streptococci mutans, (C) Streptococci pneumoniae, (D) Streptococci bovis
Answer is B. Strep. mutans:

It is member of viridans streptococci ( α hemolytic).
It assumes bacillary form in acid environment.
Can synthesize acid and large polysaccharide (adhesive dextran or levan) from sucrose.