Final answer:
Viridans streptococci are characterized by being alpha-hemolytic and showing negative results for bile solubility and optochin sensitivity, hence the correct answer is (a) Negative, Negative for their key characteristics.
Step-by-step explanation:
The viridans group streptococci are a group of Streptococcus species that are typically alpha-hemolytic and exhibit negative results for both bile solubility and optochin sensitivity tests. These characteristics help to distinguish them from other streptococci such as Streptococcus pneumoniae, which is bile soluble and optochin sensitive.
The appropriate answer to the characteristics of viridans streptococci is therefore (a) Negative, Negative as they are not lysed by bile and do not respond to optochin.