Final answer:
Streptococcus pyogenes is not a common flora of oral soft tissue.
Step-by-step explanation:
The correct answer is d) Streptococcus pyogenes.
All of the given options, streptococcus mutans, streptococcus sanguis, streptococcus salivarius, and streptococcus pyogenes, are types of streptococci that commonly inhabit oral soft tissues. However, streptococcus pyogenes is not a part of the normal oral flora. It is a pathogenic species that can cause various infections, including strep throat and skin infections.