What is the most common causative pathogen in all types of infective endocarditis, and what is the antibiotic of choice?

a) Streptococcus viridans; Penicillin
b) Staphylococcus aureus; Vancomycin
c) Enterococcus faecalis; Ampicillin
d) Streptococcus pneumoniae; Ceftriaxone